A method for treating contaminated soil

Abstract

The present invention provides a method for treating contaminated soil, which relates to the field of environmental protection. The treatment method includes the following steps: (1) crushing and sieving the soil; (2) mixing the sieved soil with a curing agent, adding material A, and continuing to mix; (3) mixing the soil obtained in step (2) with water to obtain a mixture, extruding and drying the mixture; the curing agent includes bentonite, iron oxide and diatomite, and the material A includes polyacrylamide, chitin, straw and plant extract. The treatment method of the present invention is simple, efficient and low-cost, can effectively fix heavy metals such as chromium, lead and nickel, reduces the possibility of release of heavy metals in the treated soil, and will not cause secondary pollution.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection, and specifically relates to a method for treating contaminated soil. Background Art

[0002] The causes of soil environmental pollution are complex, mainly including industrial pollution, agricultural pollution, and domestic pollutant pollution. Compared with other types of environmental pollution problems, soil pollution has the characteristics of concealment, accumulation, long-term nature, and difficulty in restoration. At present, effective remediation measures for contaminated soil include chemical remediation, physical remediation, and biological remediation. Among them, physical remediation is a type of technical means that uses physical principles and related engineering technologies to remove and transform pollutants in the soil, specifically including the soil replacement method and the incineration method. Biological remediation refers to using organisms as the main body to continuously absorb, degrade, and transform substances in the soil, gradually reducing the content of pollutants in the soil, and ultimately achieving the purpose of remediating contaminated soil, specifically including microbial remediation technology and phytoremediation technology. Chemical remediation is based on the principle of chemical decomposition or fixation reaction, adding specific substances to the contaminated soil, thereby changing the structure of soil pollutants, decomposing them into non-polluting substances, or effectively reducing the mobility and toxicity of pollutants, specifically including leaching technology and solvent extraction technology.

[0003] Among many remediation methods, the chemical remediation technology is widely used due to its short remediation cycle and good remediation effect. For example, Patent CN111940495A discloses a method for treating heavy metal contaminated soil, which specifically includes the following steps: a) mixing heavy metal contaminated soil and plant extract, granulating to obtain micro pellets; the plant extract contains carboxyl groups, hydroxyl groups, and polycyclic hydrocarbon groups; b) piling up the micro pellets to obtain a micro pellet pile; c) leaching the micro pellet pile to obtain treated soil. This method does not require the use of high-end crushing and screening, solid-liquid separation equipment, nor does it need to consider the solidification / stabilization treatment and backfilling of soil fines, and the cost is relatively low. However, the method for treating heavy metal contaminated soil in the invention uses the leaching method, which requires a large amount of water resources. At the same time, the leached liquid contains a high content of heavy metals, which will further cause water pollution.

[0004] In view of the problem of secondary pollution existing in the leaching method or solvent extraction technology, the prior art such as Patent CN102601108A discloses a method for treating arsenic-contaminated soil, which specifically includes the following steps: mixing the contaminated soil and NaOH solution to form a semi-solid system, and oxidizing the low-valent arsenic in the soil under the semi-solid system; adding iron salt to the oxidized contaminated soil and mixing and stirring for reaction. This treatment method forms a semi-solid system by stirring and mixing the contaminated soil with NaOH solution, oxidizes low-valent arsenic under the semi-solid system and alkaline conditions, and then combines ferric salt with pentavalent arsenic to generate a stable compound, ferric arsenate. This invention can complete the treatment of arsenic-contaminated soil without completely leaching arsenic. After conducting a leaching toxicity test on the treated soil, the arsenic content in the leachate is lower than 1 mg / L, meeting the national standard. Another example is Patent CN104070056A, which discloses a stabilization treatment method for heavy metal-contaminated soil, specifically including the following steps: (1) excavating heavy metal-contaminated soil, drying it in the sun and then putting it into a ball mill, and at the same time adding clay minerals with a mass fraction of 0.4-1% for ball milling; (2) after the ball milling in step (1) is completed, adding a calcium salt with a mass fraction of 0.2-0.8% and a surfactant with a mass fraction of 0.02-0.2% into the ball mill, and the soil in the ball mill continues to roll and grind for 10-20 minutes to adjust the soil moisture content; (3) backfilling the soil treated in step (2) into the foundation pit and tamping it. The method of this invention uses physical impact and bonding methods to wrap and stabilize exogenous heavy metal pollutants inside soil aggregates, reducing the release of heavy metals to achieve the stabilization effect.

[0005] In view of the problems existing in the prior art, it is very necessary to find a treatment method with little environmental pollution and capable of effectively treating contaminated soil. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for treating contaminated soil. This treatment method is simple, efficient and low-cost, can effectively fix heavy metals such as chromium, lead and nickel, reduces the possibility of heavy metal release in the treated soil, and will not cause secondary pollution.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for treating contaminated soil, including the following steps:

[0009] (1) Crushing and sieving the soil;

[0010] (2) After mixing the sieved soil with a curing agent, adding Material A and continuing to mix;

[0011] (3) Mix the soil and water obtained in step (2) to obtain a mixture, and extrude and dry the mixture.

[0012] The curing agent includes bentonite, iron oxide and diatomaceous earth, and the material A includes polyacrylamide, chitin, straw and plant extract.

[0013] Further, by weight, the curing agent includes 20-30 parts of bentonite, 3-5 parts of iron oxide and 10-15 parts of diatomaceous earth.

[0014] Preferably, by weight, the curing agent includes 25 parts of bentonite, 4 parts of iron oxide and 12 parts of diatomaceous earth.

[0015] Further, by weight, the material A includes 1-3 parts of polyacrylamide, 3-6 parts of chitin, 5-10 parts of straw and 1-2 parts of plant extract.

[0016] Preferably, by weight, the material A includes 2 parts of polyacrylamide, 5 parts of chitin, 8 parts of straw and 1.5 parts of plant extract.

[0017] Further, the preparation method of the curing agent includes: mixing bentonite, iron oxide and diatomaceous earth to obtain it; the preparation method of the material A includes mixing polyacrylamide, chitin, straw and plant extract to obtain it.

[0018] Further, the mesh number of the sieving in step (1) is 90-110 meshes; preferably 100 meshes.

[0019] Further, in step (2), the weight ratio of the soil to the curing agent is (70-100):(1-5), and the weight ratio of the soil to the material A is (70-100):(0.5-1).

[0020] Preferably, in step (2), the weight ratio of the soil to the curing agent is 30:1, and the weight ratio of the soil to the material A is 90:1.

[0021] Further, in step (3), the water content of the mixture is 10-15%; preferably 12%.

[0022] Further, in step (3), the extrusion pressure is 400-500 MPa; preferably 450 MPa.

[0023] Further, the plant extract is the extract of Sapindus mukorossi pericarp and Enteromorpha prolifera.

[0024] Further, the weight ratio of the Sapindus mukorossi pericarp to the Enteromorpha prolifera is 1:(5-10), preferably 1:6.

[0025] Further, the preparation method of the sapindus peel and enteromorpha prolifera extract includes the following steps:

[0026] Crush the dried sapindus peel and enteromorpha prolifera, add them to water and soak for 1 h (solid-liquid ratio is 100 g: 1 L), boil over high heat and then turn to low heat for 1 - 2 h, filter to obtain the extract, and concentrate the extract to a relative density of 1.5 (50 °C) to obtain the product.

[0027] Further, the treatment method can be used to treat heavy metals in soil.

[0028] Further, the heavy metals include, but are not limited to, one or more of chromium, lead, and nickel.

[0029] Further, after being treated by the treatment method, the soil can be backfilled into the foundation pit, or sintered bricks can be prepared for reuse.

[0030] The technical effects achieved by the present invention are as follows:

[0031] The treatment method of the present invention treats the soil by adding a curing agent and a specific stability material to the contaminated soil. The treatment method is simple, efficient and low-cost. By adding a small amount of curing agent and Material A (i.e., polyacrylamide, chitin, straw and plant extract, which mainly plays a stabilizing role), and using the enteromorpha prolifera extract and sapindus peel extract as the plant extract, the components in the plant extract are fully utilized, which is more environmentally friendly and avoids leaching operations in the later stage, and will not cause secondary pollution. The treatment method in the present invention can effectively fix heavy metals such as chromium, lead and nickel, reduce the possibility of heavy metal release in the treated soil, the treated soil can be backfilled or sintered bricks can be prepared for secondary utilization according to actual needs. In addition, the utilization of enteromorpha prolifera also has important significance for the direction of waste resource utilization. Description of the Drawings

[0032] Figure 1 Arsenic leaching concentrations of soil at different times after being treated by the treatment methods of each example and comparative example. Detailed Embodiments

[0033] The following specifically illustrates the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific embodiments rather than for limiting the scope of protection of the present invention.

[0035] When the embodiment gives a numerical range, it should be understood that, unless otherwise specified in the present invention, the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs.

[0036] It is worth noting that the raw materials used in the present invention are all common commercially available products, so their sources are not specifically limited.

[0037] Example 1

[0038] A method for treating contaminated soil, characterized in that it comprises the following steps:

[0039] (1) Crush the soil and pass it through a 90-mesh sieve;

[0040] (2) After mixing the sieved soil with the curing agent, add material A and continue mixing, wherein the weight ratio of the soil to the curing agent is 70:1, and the weight ratio of the soil to the material A is 70:0.5;

[0041] (3) mixing the soil obtained in step (2) with water to obtain a mixture (the water content of the mixture is adjusted to 10%), extruding the mixture (at a pressure of 400 MPa) and drying;

[0042] Among them, the curing agent includes 20 parts of bentonite, 3 parts of iron oxide and 10 parts of diatomaceous earth, and the preparation method is: mix bentonite, iron oxide and diatomaceous earth. Material A includes 1 part of polyacrylamide, 3 parts of chitin, 5 parts of straw and 1 part of soapberry peel and enteromorpha extract, and the preparation method is: mix polyacrylamide, chitin, straw and plant extract. The preparation method of soapberry peel and enteromorpha extract includes the following steps: crush the dried soapberry peel and enteromorpha in a weight ratio of 1:5, add them to water and soak for 1h (solid-liquid ratio is 100g:1L), turn from high heat to low heat and boil for 1h, filter to obtain the extract, and concentrate the extract to a relative density of 1.5 (50℃).

[0043] Example 2

[0044] A method for treating contaminated soil, characterized in that it comprises the following steps:

[0045] (1) Crush the soil and pass it through a 110-mesh sieve;

[0046] (2) After screening the soil and mixing it with the curing agent, add Material A and continue mixing. Among them, the weight ratio of the soil to the curing agent is 100:5, and the weight ratio of the soil to Material A is 100:1;

[0047] (3) After mixing the soil obtained in step (2) with water, a mixture is obtained (the water content of the mixture is adjusted to 15%). Extrude the mixture into a shape (the pressure is 500 MPa) and dry it;

[0048] Among them, the curing agent includes 30 parts of bentonite, 5 parts of iron oxide and 15 parts of diatomite. The preparation method is: mix bentonite, iron oxide and diatomite to obtain it. Material A includes 3 parts of polyacrylamide, 6 parts of chitin, 10 parts of straw, 2 parts of sapindus peel and enteromorpha prolifera extract. The preparation method is: mix polyacrylamide, chitin, straw and plant extract to obtain it. The preparation method of the sapindus peel and enteromorpha prolifera extract includes the following steps: crush the dry sapindus peel and enteromorpha prolifera with a weight ratio of 1:10, add them to water and soak for 1 h (the solid-liquid ratio is 100 g: 1 L), boil over high heat and then turn to low heat for 2 h, filter to obtain the extract, and concentrate the extract to a relative density of 1.5 (50 °C) to obtain it.

[0049] Example 3

[0050] A method for treating contaminated soil, characterized in that it includes the following steps:

[0051] (1) Crush the soil and sieve it through a 100-mesh sieve;

[0052] (2) After screening the soil and mixing it with the curing agent, add Material A and continue mixing. Among them, the weight ratio of the soil to the curing agent is 30:1, and the weight ratio of the soil to Material A is 90:1;

[0053] (3) After mixing the soil obtained in step (2) with water, a mixture is obtained (the water content of the mixture is adjusted to 12%). Extrude the mixture into a shape (the pressure is 450 MPa) and dry it;

[0054] Among them, the curing agent includes 25 parts of bentonite, 4 parts of iron oxide and 12 parts of diatomite. The preparation method is: mix bentonite, iron oxide and diatomite to obtain it. Material A includes 2 parts of polyacrylamide, 5 parts of chitin, 8 parts of straw, 1.5 parts of sapindus peel and enteromorpha prolifera extract. The preparation method is: mix polyacrylamide, chitin, straw and plant extract to obtain it. The preparation method of the sapindus peel and enteromorpha prolifera extract includes the following steps: crush the dry sapindus peel and enteromorpha prolifera with a weight ratio of 1:6, add them to water and soak for 1 h (the solid-liquid ratio is 100 g: 1 L), boil over high heat and then turn to low heat for 1.5 h, filter to obtain the extract, and concentrate the extract to a relative density of 1.5 (50 °C) to obtain it.

[0055] Comparative Example 1

[0056] The only difference from Example 3 is that the plant extract is a soapberry peel extract (the dosage is consistent with the dosage of the soapberry peel and enteromorpha extract in Example 3, and the preparation method comprises the following steps: crushing the dried soapberry peel with a weight ratio of 1:6, adding it to water and soaking it for 1h (solid-liquid ratio is 100g:1L), decocting it from high heat to low heat for 1.5h, filtering to obtain the extract, and concentrating the extract to a relative density of 1.5 (50°C)).

[0057] Comparative Example 2

[0058] The only difference from Example 3 is that the plant extract is Enteromorpha extract (the dosage is consistent with the dosage of the Enteromorpha extract of the peel and soapberry fruit in Example 3, and the preparation method comprises the following steps: crushing the dried Enteromorpha with a weight ratio of 1:6, adding it to water and soaking it for 1h (solid-liquid ratio is 100g:1L), decocting it from high heat to low heat for 1.5h, filtering to obtain the extract, and concentrating the extract to a relative density of 1.5 (50°C)).

[0059] Comparative Example 3

[0060] The difference from Example 3 is that the curing agent is 25 parts of bentonite, 4 parts of iron oxide and 12 parts of fly ash, and the material A is 2 parts of polyacrylamide, 5 parts of boric acid, 8 parts of straw and 1.5 parts of soapberry peel and Dunaliella extract (the preparation method of the extract is the same as that of Example 3, the only difference is that Enteromorpha is replaced by Dunaliella). Experimental study on the effect of the treatment method of the present invention on arsenic

[0061] 1. Test materials:

[0062] The soil was selected from yellow soil (collected from Guiyang, Guizhou, naturally air-dried after sampling, plant roots, gravel and other debris removed, and stirred evenly). The physical and chemical properties of the soil are shown in the following table:

[0063] Table 1 Physical and chemical properties of sampled soil

[0064] Physical and chemical properties pH Organic matter (g / kg) CEC (cmol / kg) Value 7.05 10.36 16.20

[0065] Pure water, concentrated sulfuric acid (superior purity, ρ = 1.84 g / ml), concentrated nitric acid (superior purity, ρ = 1.42 g / ml), dilute nitric acid (prepared by diluting concentrated nitric acid);

[0066] The leaching agent is specifically a mixture of concentrated sulfuric acid and concentrated nitric acid in a mass ratio of 2:1, added to reagent water (about 2 drops of the mixture per 1L of water) to make the pH = 3.20 ± 0.05.

[0067] 2. Preparation of Arsenic-contaminated Soil

[0068] Prepare a sodium arsenite solution with a concentration of 150 mg / L and add it to the soil that has passed through a 100-mesh sieve. The weight ratio of water to soil is 2:1. Adsorb for 4 days at 25 °C, wash the soil with pure water and then dry it for standby. After testing, the total arsenic content in the natural soil is 18.35 mg / kg, and the total arsenic content in the arsenic-contaminated soil is 145.26 mg / kg.

[0069] Experiment 1: Evaluation of stabilization rate

[0070] The specific leaching method is as follows: Take 100 g of arsenic-contaminated soil before treatment and after being treated by the treatment methods of each example and comparative example respectively, place them in a 2-L extraction bottle, calculate the volume of the leaching solution according to the solid-liquid ratio = 10 L: 1 kg based on the moisture content of the sample, mix the leaching agent with each group of samples, shake for 20 h at 25 °C, filter through a 0.5-mm filter membrane, wash the filtration device and the filter membrane with dilute nitric acid, discard the washing solution, filter and collect the leachate, store it at 4 °C and detect it using ICP-MS, and calculate the stabilization rate of arsenic. The calculation method is as follows:

[0071] The stabilization rate of arsenic = (the leaching concentration of arsenic in the soil before treatment - the leaching concentration of arsenic in the soil after treatment) / the leaching concentration of arsenic in the soil before treatment × 100%.

[0072] Statistical results are shown in Table 2.

[0073] Table 2 Stabilization rate of arsenic

[0074] Example Stabilization rate of arsenic (%) Example 1 91.7 Example 2 93.4 Example 3 94.6 Comparative example 1 85.3 Comparative example 2 80.8 Comparative example 3 73.5

[0075] As can be seen from the above table, the treatment method in the present invention can achieve a stabilization rate of arsenic above 90%. In contrast, the stabilization rate of arsenic in each comparative example is significantly lower than that in each example, indicating that the specific components of the curing agent and material A have a greater impact on the stabilization rate of arsenic, among which the plant leaching solution is especially significant.

[0076] Experiment 2: Evaluation of long-term effectiveness test

[0077] For each example group, take 5 kg of arsenic-contaminated soil and treat the soil using the treatment method of each example. Samples are taken on the 10th, 30th, and 60th days respectively. After the samples are freeze-dried, sieved and ground to 100 meshes, the concentration of available arsenic is measured with reference to the method of HJ / T 299-2007. The results of the arsenic leaching concentration in the soil at different times after being treated by the treatment methods of each example and comparative example are shown in detail in Figure 1 .

[0078] According to Figure 1It can be seen that the treatment methods of Examples 1-3 in the present invention have long-term effectiveness. At the 60th day, the leaching concentration of arsenic in the soil can still remain at a low level, and the fluctuations of the leaching concentration of arsenic at the 10th day, 30th day, and 60th day are small. In contrast, the long-term effectiveness of the treatment methods in Comparative Examples 1-3 is poor, and the soil leaching situation shows a significant increase at the 60th day.

[0079] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for treating contaminated soil, characterized in that: Specifically, the steps are as follows: (1) Crush and sieve the soil; (2) After mixing the sieved soil with the curing agent, add Material A and continue mixing; (3) Mix the soil obtained in step (2) with water to obtain a mixture, and extrude and dry the mixture; By weight, the curing agent is 20-30 parts of bentonite, 3-5 parts of iron oxide and 10-15 parts of diatomaceous earth; By weight, Material A is 2 parts of polyacrylamide, 5 parts of chitin, 8 parts of straw and 1.5 parts of plant extract; In step (2), the weight ratio of the soil to the curing agent is (70-100):(1-5), and the weight ratio of the soil to Material A is (70-100):(0.5-1); The plant extract is a sapindus peel and enteromorpha prolifera extract with a weight ratio of 1:

6.

2. The processing method according to claim 1, wherein: By weight, the curing agent is 25 parts of bentonite, 4 parts of iron oxide and 12 parts of diatomaceous earth.

3. The processing method according to claim 1, wherein: The mesh number of the sieving in step (1) is 90-110 meshes.

4. The processing method according to claim 1, wherein: In step (3), the water content of the mixture is 10-15%.

5. The processing method according to claim 1, wherein: In step (3), the extrusion pressure is 400-500 MPa.

Images