阅读说明：本技术 一种应用于重度镉污染土壤的专用固化剂及其应用方法 (Special curing agent applied to soil with severe cadmium pollution and application method thereof ) 是由 方利强 陈林华 郭佳 马嘉伟 柳丹 蔡飞 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种应用于重度镉污染土壤的专用固化剂及其应用方法,该专用固化剂的pH值为9～12；以重量份数计,包括以下组分：水泥30～50份；煅烧贝壳粉20～30份；生物炭10～20份；聚丙烯纤维2～10份；聚硫酸铁8～12份。本发明采用水泥、煅烧贝壳粉、生物炭、聚丙烯纤维和聚硫酸铁进行组合,得到的专用固化剂不仅能够提高重度镉污染土壤的抗压强度,防止开裂和二次泥化,而且显著提高重金属镉的固化性能,降低重金属镉的浸出浓度,使得土壤在长时间老化的过程中不再释放出重金属镉。(The invention discloses a special curing agent applied to soil with severe cadmium pollution and an application method thereof, wherein the pH value of the special curing agent is 9-12; the paint comprises the following components in parts by weight: 30-50 parts of cement; calcining 20-30 parts of shell powder; 10-20 parts of biochar; 2-10 parts of polypropylene fiber; 8-12 parts of ferric polysulfate. According to the invention, cement, calcined shell powder, biochar, polypropylene fiber and polyferric sulfate are combined, and the obtained special curing agent can improve the compressive strength of the soil with severe cadmium pollution, prevent cracking and secondary argillization, remarkably improve the curing performance of heavy metal cadmium, reduce the leaching concentration of heavy metal cadmium, and enable the soil not to release heavy metal cadmium any longer in the long-time aging process.)

1. The special curing agent for repairing the soil heavily polluted by cadmium is characterized in that the pH value of the special curing agent is 9-12; the paint comprises the following components in parts by weight:

2. the special curing agent for the soil heavily polluted by cadmium as claimed in claim 1, wherein the cement is portland cement; the chemical composition of the portland cement is as follows in percentage: 59-60% of CaO and Al₂O₃5.0～6.0％，SiO₂24.0～25.0％，Fe₂O₃ 3.0～4.0％，K₂O 0.5～1.0％，SO₃ 4.0～5.0％。

3. The special curing agent for soil heavily polluted by cadmium as claimed in claim 1, wherein the processing method of calcining shell powder is as follows:

(1) cleaning shell with distilled water, and oven drying at 100 deg.C to constant weight;

(2) grinding the dried shells into powder, and sieving the powder by a sieve of 60-80 meshes;

(3) calcining the screened shell powder in a muffle furnace at 1100-1300 ℃ for 2-3 hours;

(4) and (3) taking out the calcined solid, grinding the calcined solid into powder, and sieving the powder by a sieve of 60-80 meshes to obtain the processed shell powder.

4. The special curing agent for soil with severe cadmium pollution as claimed in claim 1, wherein the biochar is obtained by microwave pyrolysis treatment of peanut shells as raw materials.

5. The special curing agent for the soil with severe cadmium pollution as claimed in claim 4, wherein the preparation method of the biochar comprises the following steps:

(A) taking peanut shells, cleaning, drying and crushing to obtain peanut shell powder;

(B) and (3) performing microwave pyrolysis treatment on the peanut shell powder in the nitrogen atmosphere, and grinding the peanut shell powder into powder to obtain pyrolyzed biochar.

6. The special curing agent for soil with severe cadmium pollution as claimed in claim 5, wherein in the preparation process of the biochar, the temperature is raised to 500-600 ℃ for microwave pyrolysis for 2-3 h, and then the biochar is placed in argon gas for cooling.

7. The special curing agent for the soil with heavy cadmium pollution as claimed in claim 1, wherein the polypropylene fiber is maleic anhydride grafted polypropylene fiber after maleic anhydride grafting modification treatment;

the preparation method of the maleic anhydride polypropylene fiber comprises the following steps:

(a) adding maleic anhydride, polypropylene fiber and xylene into a bottle, and mixing to obtain a mixed solution;

(b) under the condition of nitrogen, placing the mixed solution on a heating plate, heating to 50 +/-2 ℃, physically stirring, and swelling for 30-40 min at constant temperature;

(c) adjusting the temperature of an electric heating plate, rapidly heating to 80-90 ℃, and reacting at constant temperature for 4-5 h to ensure that the xylene solution and the residual solvent are completely removed;

(d) after the reaction is completed, acetone is used for extraction, and vacuum drying is carried out at the temperature of 60 ℃ to obtain the maleic anhydride polypropylene fiber.

8. The special curing agent for the soil with heavy cadmium pollution, which is prepared from the following components in parts by weight, wherein the special curing agent has a pH value of 10:

9. the method for repairing the soil heavily polluted by cadmium by using the special curing agent as defined in any one of claims 1 to 8, which comprises the following steps: uniformly mixing the special curing agent with the soil heavily polluted by cadmium, and repairing the soil; wherein the mass ratio of the special curing agent to the soil heavily polluted by cadmium is controlled to be 3: 11-19; the water content of the mixture of the special curing agent and the heavily cadmium-polluted soil is 27-32%.

Technical Field

The invention relates to the technical field of soil heavy metal pollution solidification, in particular to a special curing agent applied to soil with severe cadmium pollution and an application method thereof.

Background

With the rapid development of industrialization and urbanization in China, the problem of heavy metal pollution of soil is increasingly serious, the quality of cultivated land is seriously reduced, and the cultivated land can enter a food chain to influence the quality and safety of crops, so that the sustainable development of society and economy is seriously threatened. Investigation of the national soil pollution survey bulletin in 2014 shows that the total national soil standard exceeding rate is 16.1%, the point standard exceeding rate of heavy metal Cd is as high as 7.0%, wherein the heavy pollution accounts for 0.5%, and the heavy pollution is positioned at the first of all pollutants. Therefore, the development of remediation for the heavy cadmium contaminated soil becomes a key problem to be urgently solved.

The current soil cadmium pollution remediation technology mainly comprises phytoremediation, in-situ remediation, leaching remediation, electrodynamic remediation and solidification remediation. The method has the advantages of environmental protection and no secondary pollution, but has the defects of low restoration efficiency, long restoration period, application only in slightly polluted areas and the like; the in-situ remediation is a method for reducing the biological effectiveness of cadmium element by adding a stabilizing material into cadmium-polluted soil, although the method can effectively reduce the absorption and enrichment of cadmium in the soil by crops, the destructive influence on the characteristics of soil structure, physicochemical property, fertility and the like is easily generated by adding the stabilizing material for a long time, and the method is only applied to areas with light and medium cadmium pollution; the leaching remediation is a method for removing cadmium elements in soil by leaching by using activating agents such as chelating agents as leacheate, and the like, and the method is high in remediation efficiency and short in remediation time period, but the method is high in remediation cost and easy to cause secondary pollution; the electrodynamic force restoration is a method for removing cadmium elements in soil by applying an external electric field through an external electrode and driving cadmium ions in the soil to migrate towards a specific direction through the actions of electromigration, electric drive and the like, and the method has small destructiveness on the soil structure and is not easy to generate secondary pollution, but is not suitable for popularization and restoration of large-area cadmium-polluted soil; the curing and repairing method is simple, high in repairing efficiency, suitable for repairing and utilizing the soil with severe cadmium pollution and high in application prospect and potential.

The invention patent application with the application publication number of CN106701088A discloses a composite curing agent for repairing heavy metal contaminated soil and an application method thereof. The composite curing agent mainly comprises curing agent liquid (water glass) and curing agent powder (calculated by mass parts, 3 parts of quicklime, 3 parts of steel slag powder, 2 parts of phosphate and 3 parts of cement), and has the advantages of simple preparation process, wide material source, good repairing effect and the like. However, the cadmium-polluted soil repaired by the curing agent has poor pressure resistance and is easy to crack and secondary argillization. In addition, due to the characteristics of strong mobility and the like of cadmium elements, the repaired cadmium-polluted soil is easy to release cadmium again in the long-time aging process, and further secondary pollution is caused.

Therefore, it is necessary to develop a special curing agent for heavy cadmium pollution to overcome the defects of the current curing agent.

Disclosure of Invention

The invention aims to overcome the defects in the application of the current heavy metal contaminated soil curing agent, and provides a special curing agent applied to heavy cadmium contaminated soil and an application method thereof.

The specific technical scheme is as follows:

a special curing agent for soil with severe cadmium pollution has a pH value of 9-12; the paint comprises the following components in parts by weight:

further, the cement is portland cement; the chemical composition of the portland cement is as follows in percentage: 59-60% of CaO and Al₂O₃ 5.0～6.0％，SiO₂ 24.0～25.0％，Fe₂O₃ 3.0～4.0％，K₂O 0.5～1.0％，SO₃4.0 to 5.0 percent. The cement prepared according to the proportion has good compressive strength.

Tests show that the leaching concentration of heavy metal cadmium can be reduced by calcining the obtained shell powder; further, the processing method for calcining the shell powder comprises the following steps:

(1) cleaning shell with distilled water, and oven drying at 100 deg.C to constant weight;

(2) grinding the dried shells into powder, and sieving the powder by a sieve of 60-80 meshes;

(3) calcining the screened shell powder in a muffle furnace at 1100-1300 ℃ for 2-3 hours;

(4) and (3) taking out the calcined solid, grinding the calcined solid into powder, and sieving the powder by a sieve of 60-80 meshes to obtain the processed shell powder.

Furthermore, the biochar is obtained by taking peanut shells as raw materials and performing microwave pyrolysis treatment. Tests show that the biochar not only can improve the compressive strength of the soil polluted by the heavy cadmium and prevent cracking and secondary argillization, but also can obviously improve the curing performance of the heavy metal cadmium and reduce the leaching concentration of the heavy metal cadmium.

Further, the preparation method of the biochar comprises the following steps:

(A) taking peanut shells, cleaning, drying and crushing to obtain peanut shell powder;

(B) and (3) performing microwave pyrolysis treatment on the peanut shell powder in the nitrogen atmosphere, and grinding the peanut shell powder into powder to obtain pyrolyzed biochar.

Further, in the preparation process of the biochar, the temperature is increased to 500-600 ℃ for microwave pyrolysis for 2-3 hours, and then the biochar is placed in argon for cooling.

Before the microwave pyrolysis process, nitrogen is firstly introduced to ensure the anaerobic condition in the preparation process. The nitrogen flow was 30mL/min for 10 min.

Because different temperatures and heating rates can affect the space structure, specific surface area, the number of surface functional groups and other characteristic characteristics of the biochar of the peanut shells, the efficiency of adsorbing the cadmium in the soil is further affected. Therefore, in order to maximize the adsorption performance of the peanut shell biochar, the preparation temperature of the peanut shell biochar is 550 ℃, the pyrolysis time is 2 hours when the temperature peak is reached, and then the peanut shell biochar is cooled in argon. The prepared peanut shell biochar is ground into powder and is sieved by a 100-mesh sieve for later use.

The peanut shell biochar disclosed by the invention adopts peanut shells produced in the same season as a raw material, the peanut shells are cleaned by distilled water and then dried in an oven at 80 ℃ to constant weight, and then the peanut shells are crushed into solids of 1 multiplied by 1cm by a small crusher and used for preparing the peanut shell biochar.

Further, the polypropylene fiber is maleic anhydride polypropylene fiber which is subjected to maleic anhydride grafting modification treatment; the leaching concentration of the heavy metal cadmium can be further reduced.

Further, the preparation method of the modified polypropylene fiber comprises the following steps:

(a) adding maleic anhydride, polypropylene fiber and xylene into a bottle, and mixing to obtain a mixed solution;

(b) under the condition of nitrogen, placing the mixed solution on a heating plate, heating to 50 +/-2 ℃, physically stirring, and swelling for 30-40 min at constant temperature;

(c) adjusting the temperature of an electric heating plate, rapidly heating to 80-90 ℃, and reacting at constant temperature for 4-5 h to ensure that the xylene solution and the residual solvent are completely removed;

(d) after the reaction is completed, acetone is used for extraction, and vacuum drying is carried out at the temperature of 60 ℃ to obtain the maleic anhydride polypropylene fiber.

Further, the ferric polysulfate is ground into powder and is used after being screened by a 100-mesh sieve.

Preferably, the special curing agent has a pH value of 10, and comprises the following components in parts by weight:

the invention also provides a method for repairing the soil with severe cadmium pollution by using the special curing agent, which comprises the following steps: adding water to uniformly mix the special curing agent with the soil heavily polluted by cadmium, and repairing the soil; wherein the mass ratio of the special curing agent to the soil heavily polluted by cadmium is controlled to be 3: 11-19; the water content of the mixture of the special curing agent and the heavily cadmium-polluted soil is 27-32%.

The soil remediation can be ex-situ remediation, namely, the soil with severe cadmium pollution to be remedied is taken out to be mixed with a special curing agent, and then the mixture is pressed and molded; or in-situ remediation, namely, the special curing agent is scattered into the soil with severe cadmium pollution, and the soil is turned and stirred, so that the special curing agent and the soil with severe cadmium pollution are uniformly mixed.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, cement, calcined shell powder, biochar, polypropylene fiber and polyferric sulfate are combined, and the obtained special curing agent can improve the compressive strength of the soil with severe cadmium pollution, prevent cracking and secondary argillization, remarkably improve the curing performance of heavy metal cadmium, reduce the leaching concentration of heavy metal cadmium, and enable the soil not to release heavy metal cadmium any longer in the long-time aging process.

Detailed Description

The present invention will be further described with reference to the following specific examples, which are only illustrative of the present invention, but the scope of the present invention is not limited thereto.

The cadmium-polluted soil required by the test is collected from surface soil (0-20 cm) near a certain mining area in Shaoxing city, Zhejiang province, is naturally air-dried, plant residues and stones are removed, and the cadmium-polluted soil is ground and sieved by a 100-mesh sieve for later use. The leaching concentration of heavy metal cadmium in the soil sample before restoration is 1.69 mg/L.

Unconfined compressive strength test the compressive strength of the restored soil is tested according to road geotechnical test regulation (JTG E40-2007). The soil samples before and after the test were tested according to the sulfuric acid-nitric acid method (HJ/T299-2007) of leaching toxicity of solid wastes, and the ion concentration of cadmium in the filtrate was measured by using a graphite furnace atomic absorption spectrometer. And finally, determining and analyzing the content of the leached cadmium according to 'hazardous waste identification standard leaching toxicity identification' (GB 5085.3-2007).

Example 1

The special curing agent for the soil with severe cadmium pollution comprises the following components in parts by weight:

40 parts of Portland cement, 25 parts of calcined shell powder, 15 parts of peanut shell biochar, 5 parts of maleic anhydride polypropylene fiber and 10 parts of ferric polysulfate, and the pH value is 10. The raw materials are stirred for 5 hours by a small stirrer after being mixed, and the components are ensured to be fully mixed.

Wherein the chemical composition of the portland cement is as follows: 59-60% of CaO and Al₂O₃ 5.0～6.0％，SiO₂ 24.0～25.0％，Fe₂O₃ 3.0～4.0％，K₂O 0.5～1.0％，SO₃ 4.0～5.0％。

The processing method for calcining the shell powder comprises the following steps:

(1) cleaning shell with distilled water, and oven drying at 100 deg.C to constant weight;

(2) grinding the dried shell into powder, and sieving with a 80-mesh sieve;

(3) calcining the screened shell powder in a muffle furnace at 1200 ℃ for 2.5 hours;

(4) and (3) taking out the calcined shell powder, grinding the calcined shell powder into powder, and sieving the powder by a 80-mesh sieve to obtain the processed shell powder.

The preparation method of the peanut shell biochar comprises the following steps:

(A) taking peanut shells, cleaning, drying and crushing to obtain peanut shell powder;

(B) firstly introducing nitrogen with the flow rate of 30mL/min for 10 min; heating the peanut shell powder to 550 ℃ under the nitrogen atmosphere, carrying out microwave pyrolysis treatment on the peanut shell powder for 2-3 hours, then grinding the peanut shell powder into powder, and then placing the powder in argon for cooling to obtain pyrolyzed biochar;

the preparation method of the maleic anhydride polypropylene fiber comprises the following steps:

(a) adding maleic anhydride, polypropylene fiber and xylene into a bottle, and mixing to obtain a mixed solution;

(b) under the condition of nitrogen, placing the mixed solution on a heating plate, heating to 50 +/-2 ℃, physically stirring, and swelling for 30-40 min at constant temperature;

(c) adjusting the temperature of an electric heating plate, rapidly heating to 80-90 ℃, and reacting at constant temperature for 4-5 h to ensure that the xylene solution and the residual solvent are completely removed;

(d) after the reaction is completed, acetone is used for extraction, and vacuum drying is carried out at the temperature of 60 ℃ to obtain the maleic anhydride polypropylene fiber.

Grinding ferric polysulfate into powder, and sieving with a 100-mesh sieve for use.

The steps for repairing the soil with severe cadmium pollution and detecting the performance are as follows:

1) collecting the soil heavily polluted by cadmium to be repaired, naturally drying, removing impurities such as tree roots, broken stones and the like, grinding into powder, and sieving with a 100-mesh sieve for repairing.

2) According to the mass ratio of 3:11(W special curing agent: the/W cadmium-polluted soil) adding the special curing agent and the cadmium-polluted soil into a mixing stirrer together, uniformly stirring, and spraying a certain amount of water in the stirring process to ensure that the integral water content of the mixture of the soil and the curing agent reaches 30 percent.

3) According to the one-time sample pressing forming method, a phi 50mm multiplied by 50mm sample is formed in a one-time pressing mode through a hydraulic control type press machine through a mixture of polluted soil and a curing agent, the sample is demoulded through a demould device, the sample formed in a pressing mode is placed into a freshness protection package, and finally the freshness protection package is placed into a maintenance box to be maintained for 7 days under standard conditions (20 +/-2 ℃ and humidity of 90%)), and after 28 days, sampling is carried out, and performance detection is carried out. The results are shown in tables 1 and 2.

Example 2

The curing agent provided in this example is composed of the following components in parts by weight: 30 parts of Portland cement, 30 parts of calcined shell powder, 20 parts of peanut shell biochar, 8 parts of maleic anhydride polypropylene fiber and 12 parts of ferric polysulfate, and the pH value is 10.

The mass ratio of the curing agent to the cadmium heavily-polluted soil is 3: 19. The preparation methods of other raw materials are the same as the example 1, and the steps of repairing the soil with severe cadmium pollution and detecting the performance are also the same as the example 1. The results are shown in tables 1 and 2.

Example 3

The curing agent provided in this example is composed of the following components in parts by weight: 40 parts of Portland cement, 25 parts of calcined shell powder, 20 parts of peanut shell biochar, 5 parts of maleic anhydride polypropylene fiber and 10 parts of ferric polysulfate, and the pH value is 10.

The mass ratio of the curing agent to the cadmium heavily-polluted soil is 3: 17. The preparation methods of other raw materials are the same as the example 1, and the steps of repairing the soil with severe cadmium pollution and detecting the performance are also the same as the example 1. The results are shown in tables 1 and 2.

Example 4

The curing agent provided by the comparative example consists of the following components in parts by weight: 40 parts of Portland cement, 25 parts of calcined shell powder, 15 parts of peanut shell biochar, 5 parts of polypropylene fiber and 10 parts of ferric polysulfate, and the pH value is 10. Wherein, the polypropylene fiber is not grafted and modified by maleic anhydride, the preparation method of the other raw materials is the same as that of the embodiment 1, and the steps of repairing the soil with serious cadmium pollution and detecting the performance are also the same as that of the embodiment 1. The results are shown in tables 1 and 2.

Comparative example 1

The curing agent provided by the comparative example consists of the following components in parts by weight: 40 parts of Portland cement, 25 parts of calcined shell powder, 15 parts of peanut shell biochar and 10 parts of ferric polysulfate, wherein the pH value is 10. Wherein, the component of polypropylene fiber is not adopted, the preparation method of the other raw materials is the same as that of the embodiment 1, and the steps of repairing the soil with serious cadmium pollution and detecting the performance are also the same as that of the embodiment 1. The results are shown in tables 1 and 2.

Comparative example 2

The curing agent provided by the comparative example consists of the following components in parts by weight: 40 parts of Portland cement, 25 parts of calcined shell powder, 15 parts of peanut shell biochar and 5 parts of polypropylene fiber, wherein the pH value is 10. Wherein, the component of ferric polysulfate is not adopted, the preparation method of the other raw materials is the same as that of the embodiment 1, and the steps of repairing the soil with serious cadmium pollution and detecting the performance are also the same as that of the embodiment 1. The results are shown in tables 1 and 2.

Comparative example 3

The curing agent provided by the comparative example consists of the following components in parts by weight: 40 parts of portland cement, 25 parts of shell powder, 15 parts of peanut shell biochar, 5 parts of polypropylene fiber and 10 parts of ferric polysulfate, wherein the pH value is 10. Wherein, the preparation method of the shell powder is the same as that of the embodiment 1 after the calcination, and the steps of repairing the soil with serious cadmium pollution and detecting the performance are also the same as that of the embodiment 1. The results are shown in tables 1 and 2.

The leaching concentration of the heavy cadmium contaminated soil sample before and after being treated by the special curing agent is shown in table 2, and the unconfined compressive strength of the sample before and after being treated by the special curing agent is measured in table 3.

TABLE 2 soil sample heavy metal cadmium leaching concentration (mg/L) before and after treatment with special curing agent

TABLE 3 unconfined compressive strength (MPa) of sample before and after treatment with special curing agent

Examples	Treating for 7 days	Treating for 28 days
			Example 1	24.23a	34.43a
Example 2	21.51ab	31.75ab
			Example 3	23.47ab	32.61ab
Example 4	22.34ab	30.48b
			Comparative example 1	17.59bc	26.93c
Comparative example 2	19.57b	29.41bc
			Comparative example 3	15.47c	27.47c

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