Soil cadmium and lead in-situ remediation agent and in-situ remediation method

Abstract

The invention relates to the technical field of soil remediation, in particular to a soil cadmium and lead in-situ remediation agent and an in-situ remediation method. The invention relates to a soil cadmium and lead in-situ repairing agent which comprises polyhexamethylene guanidine phosphate and an alkali-activated gel material. The polyhexamethyleneguanidine phosphate is combined with free cadmium and lead, the alkali-activated gel material fixes the polyhexamethyleneguanidine phosphate, so that the polyhexamethyleneguanidine phosphate is not prone to loss, the soil remediation period of the material is moderate, the fast-acting property is high, the free cadmium and lead on the surface layer of the soil can be combined, and the soil remediation efficiency is improved. Cadmium and lead combined by the repairing agent are not absorbed by crops.

Description

Technical Field

[0001] This application relates to the technical field of soil remediation, and particularly relates to an in-situ remediation agent and an in-situ remediation method for cadmium and lead in soil. Background Art

[0002] The accumulation of heavy metal elements such as cadmium (Cd) and lead (Pb) in farmland soil mainly stems from natural geological backgrounds and human activities. These heavy metals enter the soil environment through various channels and remain in the soil for a long time, posing a potential threat to crop safety and human health.

[0003] The existing forms of cadmium in soil are divided into water-soluble and water-insoluble cadmium. Ionic CdCl2, Cd(NO3)2, CdCO3, and complexed forms such as Cd(OH)2 are water-soluble, easily migratable, and can be absorbed by plants. Non-water-soluble cadmium, such as cadmium precipitates and cadmium adsorbed on colloids, is fixed on the surface of soil particles, not easily migratable, and not easily absorbed by plants.

[0004] There are various free and non-free forms of lead in soil, including lead sulfide (PbS), lead carbonate (PbCO3), lead sulfate (PbSO4), lead dichloride PbCl2, lead oxide PbO, organic lead, etc. Some of these leads can be directly absorbed by plants, and some leads that are not easily absorbed by plants will become easily absorbed by plants when the soil turns acidic.

[0005] The in-situ remediation method of directly applying the remediation agent to farmland soil is relatively simple and has a low remediation cost. Phosphorus-based remediation agents have important application values in the in-situ remediation of cadmium (Cd) and lead (Pb) in farmland soil, and they achieve safe utilization by passivating heavy metals and improving the soil environment.

[0006] The phosphorus-based remediation agent passivates cadmium Cd 2+ and lead Pb 2+ to form insoluble cadmium phosphate (Cd3(PO4)2) and lead phosphate (Pb3(PO4)2), reducing the bioavailability of cadmium and lead. Commonly used phosphorus-based remediation agents include potassium dihydrogen phosphate, ammonium dihydrogen phosphate, hydroxyapatite, phosphorite, etc. Potassium dihydrogen phosphate and ammonium dihydrogen phosphate are suitable for acidic to neutral soils, with strong quick-acting properties. However, phosphorus easily penetrates quickly to the deep layer of the soil or is washed away by rainwater, resulting in fast phosphorus loss. Thus, it does not fully combine with cadmium and lead in the surface soil to form precipitates, and therefore its effect of reducing the concentrations of Cd 2+ and Pb 2+ in the soil is not significant enough. Hydroxyapatite and phosphorite release phosphate slowly, have low costs, and are suitable for large-area remediation. However, they need to be combined with acidic conditions or microbial activation to maintain the remediation effect, and the remediation cycle is too long, reaching 3 to 6 months. Summary of the Invention

[0007] Based on the problems existing in some of the above phosphorus-based remediation agents for in-situ remediation of cadmium and lead contaminated soil, the present application proposes a soil remediation agent with low phosphorus loss and strong quick-acting property, as well as a method for remediating soil to solve this problem.

[0008] In the first aspect, the present application proposes a soil cadmium and lead in-situ remediation agent, and adopts the following technical solutions. A soil cadmium and lead in-situ remediation agent, comprising polyhexamethylene guanidine phosphate and an alkali-activated gel material.

[0009] By adopting the above technical solutions, polyhexamethylene guanidine phosphate binds Cd 2+ and Pb 2+ , and the alkali-activated gel material fixes the polyhexamethylene guanidine phosphate, making the polyhexamethylene guanidine phosphate not easy to lose. The period for this material to remediate the soil is about 20 - 30 days, with strong quick-acting property, and it can bind 50 - 70% of the free Cd 2+ and Pb 2+ in the soil surface layer for crop growth. The cadmium and lead bound by the remediation agent are not absorbed by crops.

[0010] A preferred scheme of the soil cadmium and lead in-situ remediation agent is that the polyhexamethylene guanidine phosphate and the alkali-activated gel material are mixed to obtain the in-situ remediation agent, and the mass ratio of the polyhexamethylene guanidine phosphate to the alkali-activated gel material is 1:(3 - 10).

[0011] By adopting the above technical solutions, the remediation agent with this ratio can fully soak the soil, which can not only keep the polyhexamethylene guanidine phosphate in the soil, but also enable the polyhexamethylene guanidine phosphate to fully bind Cd 2+ and Pb 2+ . If the proportion of the alkali-activated gel material is too high, the contact area between the polyhexamethylene guanidine phosphate and the soil will be weakened. If the proportion of the alkali-activated gel material is too low, the retention force of the polyhexamethylene guanidine phosphate in the soil will be weak.

[0012] A preferred scheme of the soil cadmium and lead in-situ remediation agent is that the alkali-activated gel material is obtained by activating fly ash and rice husk ash with an alkali solution.

[0013] By adopting the above technical solution, SiO2, Al2O3 and CaO in fly ash are the main components participating in the low-polymerization reaction. SiO2 and Al2O3 gradually dissolve under the action of alkali to form [SiO4] and [AlO4] monomers, and the monomers polymerize with each other to generate amorphous gels such as sodium aluminosilicate hydrate (N-A-S-H), sodium silicate hydrate (N-S-H) and sodium aluminate hydrate (N-A-H). The calcium-containing active components are converted into calcium silicate hydrate (C-S-H), calcium aluminate hydrate (C-A-H) and calcium aluminosilicate hydrate (C-A-S-H) amorphous gels under alkaline conditions. These gels bond the unreacted inert particles and finally dehydrate and solidify to form a dense-structured oligomer material. Rice husk ash is an important component obtained by roasting rice husks. In this ash, the silica content is as high as 80% - 95%, and SiO3 2- ions are generated under the action of alkali. SiO3 2- ions can increase the degree of polymerization of the gelling substance and promote the formation of the gelling network. The alkali solution can be a sodium hydroxide solution. This alkali-activated gel material can adhere to polyhexamethylene guanidine phosphate to make it fully contact the soil.

[0014] A preferred solution of this in-situ soil cadmium and lead remediator is that the mass percentage of the fly ash and the rice husk ash is 70 - 80%: 20 - 30%; the initial concentration of the alkali solution is 2 - 8 mol / L, and the solid-liquid ratio of the mixture of the fly ash and the rice husk ash and the alkali solution is 1 kg / (2 - 3 L).

[0015] By adopting the above technical solution, the alkali-activated gel material with this ratio fully activates the activity of fly ash and rice husk ash, enabling it to adhere to the soil and polyhexamethylene guanidine phosphate, and also adsorb Cd 2+ and Pb 2+ , promoting the combination of polyhexamethylene guanidine phosphate and Cd 2+ and Pb 2+ .

[0016] A preferred solution of this in-situ soil cadmium and lead remediator is that the activation process includes: grinding the fly ash and the rice husk ash to a specific surface area of 400 - 600 m 2 / kg, and then adding the alkali solution. After the alkali solution fully reacts with the fly ash and the rice husk ash, the alkali-activated gel material is obtained.

[0017] By adopting the above technical solution, the alkali solution fully reacts with fly ash and rice husk ash, and the obtained alkali-activated gel material can fully penetrate the soil and improve the dispersion degree of polyhexamethylene guanidine phosphate in the soil.

[0018] In the second aspect, the present application also proposes an in-situ soil cadmium and lead remediation method and adopts the following technical solutions.

[0019] A method for in-situ remediation of cadmium and lead in soil, applying the above in-situ remediation agent to the soil containing cadmium and lead, fully mixing the in-situ remediation agent and the soil, so that the in-situ remediation agent fully combines with cadmium and lead and solidifies.

[0020] By adopting the above technical solution, the in-situ remediation agent adsorbs and combines polyhexamethylene guanidine phosphate of cadmium and lead, gradually solidifies, and stably exists in the soil, no longer releasing cadmium and lead.

[0021] A preferred scheme of the method for in-situ remediation of cadmium and lead in soil is that the application amount of the in-situ remediation agent is 50 - 100 g / m 2 。

[0022] By adopting the above technical solution, this application amount can appropriately penetrate the soil surface layer and fully combine with cadmium and lead in the soil surface layer.

[0023] A preferred scheme of the method for in-situ remediation of cadmium and lead in soil is that during the process of fully mixing the in-situ remediation agent and the soil, water is also applied, and the water application amount is 1 - 5 L / m 2 。

[0024] By adopting the above technical solution, adding water promotes the dispersion of the in-situ remediation agent, enhances the penetration of polyhexamethylene guanidine phosphate into soil particles, and improves the remediation efficiency.

[0025] In summary, the in-situ remediation agent and the in-situ remediation method for cadmium and lead in soil of the present application have the following beneficial effects: the in-situ remediation agent has an appropriate effect of penetrating and adhering to soil particles, and polyhexamethylene guanidine phosphate has a high efficiency of binding cadmium and lead, and polyhexamethylene guanidine phosphate is not easily lost and has strong quick-acting properties. Description of the Drawings

[0026] Figure 1 It is a flow chart of the method for in-situ remediation of cadmium and lead in soil in Example 1. Detailed Description of the Embodiments

[0027] The technical solutions in the embodiments are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the following embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application. Example 1

[0028] Refer to Figure 1 , a method for in-situ remediation of cadmium and lead in soil, and the remediation steps are as follows.

[0029] (1) Preparation of alkali-activated gel material: The alkali-activated gel material is obtained by activating fly ash and rice husk ash with sodium hydroxide solution. The activation process is to grind fly ash and rice husk ash to a specific surface area of 500 m 2 / kg, then add sodium hydroxide solution. After the sodium hydroxide solution reacts fully with fly ash and rice husk ash, the alkali-activated gel material is obtained. Among them, the mass percentage of fly ash and rice husk ash is 75%:25%, the initial concentration of the sodium hydroxide solution is 5 mol / L, and the solid-liquid ratio of the mixture of fly ash and rice husk ash and the sodium hydroxide solution is 1 kg / 2.5 L.

[0030] (2) Preparation of in-situ repair agent: Mix 1 part by mass of polyhexamethylene guanidine phosphate and 6 parts by mass of alkali-activated gel material to obtain the in-situ repair agent.

[0031] (3) Apply the in-situ repair agent to the surface layer of soil containing cadmium and lead. The application amount of the in-situ repair agent is 75 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, spray water, and the water application amount is 3 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to fully combine with cadmium and lead and solidify. Example 2

[0032] A method for in-situ remediation of cadmium and lead in soil, and the remediation steps are as follows.

[0033] (1) Preparation of alkali-activated gel material: The alkali-activated gel material is obtained by activating fly ash and rice husk ash with sodium hydroxide solution. The activation process is to grind fly ash and rice husk ash to a specific surface area of 400 m 2 / kg, then add sodium hydroxide solution. After the sodium hydroxide solution reacts fully with fly ash and rice husk ash, the alkali-activated gel material is obtained. Among them, the mass percentage of fly ash and rice husk ash is 70%:30%, the initial concentration of the sodium hydroxide solution is 2 mol / L, and the solid-liquid ratio of the mixture of fly ash and rice husk ash and the sodium hydroxide solution is 1 kg / 2 L.

[0034] (2) Preparation of in-situ repair agent: Mix 1 part by mass of polyhexamethylene guanidine phosphate and 10 parts by mass of alkali-activated gel material to obtain the in-situ repair agent.

[0035] (3) Apply the in-situ repair agent to the surface layer of soil containing cadmium and lead. The application amount of the in-situ repair agent is 50 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, spray water, and the water application amount is 1 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to fully combine with cadmium and lead and solidify. Example 3

[0036] A method for in-situ remediation of cadmium and lead in soil, and the remediation steps are as follows.

[0037] (1) Preparation of alkali-activated gel material: The alkali-activated gel material is obtained by activating fly ash and rice husk ash with sodium hydroxide solution. The activation process is to grind fly ash and rice husk ash to a specific surface area of 600 m 2 / kg, then add sodium hydroxide solution. After the sodium hydroxide solution reacts fully with fly ash and rice husk ash, the alkali-activated gel material is obtained. Among them, the mass percentage of fly ash and rice husk ash is 80%:20%, the initial concentration of the sodium hydroxide solution is 8 mol / L, and the solid-liquid ratio of the mixture of fly ash and rice husk ash and the sodium hydroxide solution is 1 kg / 3 L.

[0038] (2) Preparation of in-situ repair agent: Mix 1 part by mass of polyhexamethylene guanidine phosphate and 3 parts by mass of alkali-activated gel material to obtain the in-situ repair agent.

[0039] (3) Apply the in-situ repair agent to the surface layer of soil containing cadmium and lead. The application amount of the in-situ repair agent is 100 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, spray water, and the water application amount is 5 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to bind cadmium and lead fully and solidify. Example 4

[0040] A method for in-situ remediation of cadmium and lead in soil. In this example, compared with Example 1, only the ratio of the in-situ repair agent is adjusted, and other parameters are the same. In this example, mix 1 part by mass of polyhexamethylene guanidine phosphate and 3 parts by mass of alkali-activated gel material to obtain the in-situ repair agent. Example 5

[0041] A method for in-situ remediation of cadmium and lead in soil. In this example, compared with Example 1, only the ratio of the in-situ repair agent is adjusted, and other parameters are the same. In this example, mix 1 part by mass of polyhexamethylene guanidine phosphate and 10 parts by mass of alkali-activated gel material to obtain the in-situ repair agent.

[0042] Comparative Example 1 In this comparative example, compared with Example 1, the use of polyhexamethylene guanidine phosphate is cancelled, as follows.

[0043] A method for in-situ remediation of cadmium and lead in soil. The remediation steps are as follows.

[0044] (1) Preparation of alkali-activated gel material: The alkali-activated gel material is obtained by activating fly ash and rice husk ash with sodium hydroxide solution. The activation process is to grind fly ash and rice husk ash to a specific surface area of 500 m 2 / kg, then add sodium hydroxide solution. After the sodium hydroxide solution reacts fully with fly ash and rice husk ash, an alkali-activated gel material is obtained. Among them, the mass percentage of fly ash and rice husk ash is 75%:25%, the initial concentration of the sodium hydroxide solution is 5 mol / L, and the solid-liquid ratio of the mixture of fly ash and rice husk ash and the sodium hydroxide solution is 1 kg / 2.5 L.

[0045] (2) Apply the in-situ repair agent to the surface layer of the soil containing cadmium and lead. The application amount of the in-situ repair agent is 75 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, and spray water. The water application amount is 3 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to adsorb cadmium and lead and solidify.

[0046] Comparative Example 2 In this comparative example compared with Example 1, the use of the alkali-activated gel material was cancelled, as follows.

[0047] A method for in-situ remediation of cadmium and lead in soil, the remediation steps are as follows.

[0048] (1) Prepare the in-situ repair agent: Use polyhexamethylene guanidine phosphate as the in-situ repair agent.

[0049] (2) Apply the in-situ repair agent to the surface layer of the soil containing cadmium and lead. The application amount of the in-situ repair agent is 75 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, and spray water. The water application amount is 3 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to combine with cadmium and lead fully.

[0050] Comparative Example 3 In this comparative example compared with Example 1, the in-situ repair agent was replaced with potassium dihydrogen phosphate, as follows.

[0051] A method for in-situ remediation of cadmium and lead in soil, the remediation steps are as follows.

[0052] Use potassium dihydrogen phosphate as the in-situ repair agent, apply the in-situ repair agent to the surface layer of the soil containing cadmium and lead. The application amount of the in-situ repair agent is 75 g / m 2 , then mix the in-situ repair agent and the soil in the surface layer with a depth of 20 cm thoroughly, and spray water. The water application amount is 3 L / m 2 , and let it stand for 25 days to allow the in-situ repair agent to combine with cadmium and lead fully and solidify.

[0053] Comparative Example 4 In this comparative example compared with Example 1, the in-situ repair agent was replaced with hydroxyapatite, as follows.

[0054] A method for in-situ remediation of cadmium and lead in soil, the remediation steps are as follows.

[0055] Using hydroxyapatite as an in-situ repair agent, the in-situ repair agent was applied to the surface layer of soil containing cadmium and lead, and the application amount of the in-situ repair agent was 75 g / m 2 , and then the in-situ repair agent was thoroughly mixed with the soil in the surface layer at a depth of 20 cm, and water was sprayed, and the water application amount was 3 L / m 2 , and it was left standing for 25 days to allow the in-situ repair agent to fully bind to cadmium and lead and solidify.

[0056] The soil sources of Examples 1 to 5 and Comparative Examples 1 to 4 above were the same.

[0057] Test Example 1 Test the changes in the concentrations of soluble cadmium and lead in the soils of Examples 1 to 5 and Comparative Examples 1 to 4 before and after repair. The test process was as follows: the soil was soaked in water, and the mass ratio of soil to water was 1:2. After thorough stirring and centrifugation, the supernatant was taken, and the contents of cadmium and lead in the supernatant were sequentially detected by atomic absorption spectrometry and converted into the cadmium and lead contents of the soil. The test results are summarized in Table 1 below.

[0058] Table 1 Changes in the contents of soluble cadmium and lead in the soil

[0059] It can be seen from Table 1 that the schemes of Examples 1 to 5 have good effects on solidifying water-soluble cadmium and lead in the soil, and the solidification rate is about 50 - 70%. By comparing Examples 1, 3, and 4, it can be seen that increasing the proportion of polyhexamethylene guanidine phosphate or increasing the dosage of the in-situ repair agent on the basis of Example 1 has limited effects. By comparing Examples 1, 2, and 5, it can be seen that reducing the proportion of polyhexamethylene guanidine phosphate and / or the dosage of the in-situ repair agent on the basis of Example 1 will slightly reduce the effects of solidifying cadmium and lead.

[0060] It can be seen from Table 1 that compared with Example 1, the effect of solidifying cadmium and lead in Comparative Example 1 is significantly reduced, indicating that polyhexamethylene guanidine phosphate in the repair agent of the present application plays a significant role in solidifying cadmium and lead. Compared with Example 1, the effect of solidifying cadmium and lead in Comparative Example 2 is reduced, indicating that the alkali-activated gel material in the repair agent of the present application plays an auxiliary role in solidifying cadmium and lead, and the alkali-activated gel material can adhere to and combine polyhexamethylene guanidine phosphate that has combined with cadmium and lead. Compared with Example 1, the effect of solidifying cadmium and lead in Comparative Example 3 is reduced, indicating that compared with potassium dihydrogen phosphate, the repair agent of the present application significantly improves the effect of solidifying cadmium and lead. Compared with Example 1, the effect of solidifying cadmium and lead in Comparative Example 4 is reduced, indicating that compared with hydroxyapatite, the repair agent of the present application significantly improves the effect of solidifying cadmium and lead.

[0061] Test Example 2 Before and after the restoration of the soil in Example 1, its pH was measured, and white radishes were planted respectively. During this period, the same maintenance conditions were used to maintain the growth of the radishes. The growth of the white radishes in the later stage was checked, and the cadmium and lead contents of the fresh radish roots were detected. The results are shown in Table 2.

[0062] Table 2 Planting Test

[0063] Table 2 shows that using the repair agent of the present application will slightly increase the pH of the soil, but the effect is not significant. For the soil polluted by cadmium and lead, after using the repair agent of the present application to repair the soil, the growth of the planted white radishes is better than that without soil repair, and the cadmium and lead contents in the radish roots are significantly reduced. The above shows that the repair agent of the present application can repair soil cadmium and lead pollution and is helpful for crop growth.

[0064] For the repair agent of the present application, polyhexamethylene guanidine phosphate can be dissolved in water, so that the phosphate group of polyhexamethylene guanidine phosphate can efficiently bind cadmium and lead. At the same time, the alkali-activated gel material can adhere polyhexamethylene guanidine phosphate and soil particles, improve the contact rate of polyhexamethylene guanidine phosphate with cadmium and lead in the soil, and improve the binding rate. The alkali-activated gel material can also gradually lose water and solidify, wrapping the polyhexamethylene guanidine phosphate combined with cadmium and lead, and no longer releasing cadmium and lead, so it is basically no longer absorbed by crops. Applying this repair agent to the repair of farmland soil has a good treatment effect.

[0065] Although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A soil cadmium and lead in-situ remediation agent, characterized in that, It contains polyhexamethylene guanidine phosphate and alkali-activated gel material.

2. The soil cadmium and lead in-situ remediation agent according to claim 1, characterized in that, Mix the polyhexamethylene guanidine phosphate and the alkali-activated gel material to obtain the in-situ repair agent, and the mass ratio of the polyhexamethylene guanidine phosphate to the alkali-activated gel material is 1:(3 - 10).

3. The soil cadmium and lead in-situ remediation agent according to claim 2, characterized in that, The alkali-activated gel material is obtained by activating fly ash and rice husk ash with an alkali solution.

4. The soil cadmium and lead in-situ remediation agent according to claim 3, characterized in that, The mass percentage of the fly ash and the rice husk ash is 70 - 80%:20 - 30%; the initial concentration of the alkali solution is 2 - 8 mol / L, and the solid-liquid ratio of the mixture of the fly ash and the rice husk ash to the alkali solution is 1 kg / (2 - 3 L).

5. The soil cadmium and lead in-situ remediation agent according to claim 3 or 4, characterized in that, The activation process includes: grinding the fly ash and the rice husk ash to a specific surface area of 400 - 600 m 2 / kg, then adding the alkali solution. After the alkali solution fully reacts with the fly ash and the rice husk ash, the alkali-activated gel material is obtained.

6. A soil cadmium and lead in-situ remediation method, characterized in that, Apply the in-situ repair agent according to any one of claims 1 - 5 to the soil containing cadmium and lead, and fully mix the in-situ repair agent and the soil so that the in-situ repair agent fully combines with cadmium and lead and solidifies.

7. The soil cadmium and lead in-situ remediation method according to claim 6, characterized in that, The application amount of the in-situ repair agent is 50~100 g / m 2 .

8. The soil cadmium and lead in-situ remediation method according to claim 6, characterized in that, During the process of fully mixing the in-situ repair agent and the soil, water is also applied, and the water application amount is 1 - 5 L / m 2 .

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