Remediation method of low-permeability fluorine-polluted bottom mud

Abstract

The invention discloses a method for repairing low-permeability fluorine-polluted bottom mud, which comprises the following steps: S1, mixing three solutions of citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine in proportion to obtain an eluting agent; s2, repairing the fluorine-polluted bottom mud: adding the eluting agent obtained in S1 into the fluorine-polluted bottom mud, and continuously stirring for 1-2 hours in an eluting and stirring box; in the leaching process, a pressurizing air pump is used for pumping air from the lower portion of a porous disc at the bottom of a leaching stirring box, and formed microbubbles are used for conducting microbubble-leaching combined enhanced remediation on the fluorine pollution bottom mud saturated through leaching; and S3, performing mud-water separation on the bottom mud repaired in the step S2 to complete leaching. The method is simple in process, convenient to operate, high in reaction speed and good in leaching effect, the leaching agent and the microbubble device are easy to obtain, and the method has a combined enhancement effect on fluorine-polluted bottom mud remediation and is suitable for fluorine-polluted remediation of low-permeability bottom mud such as clay, silty clay and floury soil.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorine-contaminated sludge restoration, and in particular relates to a method for restoring low-permeability fluorine-contaminated sludge. Background Art

[0002] A large amount of fluorine-containing waste is generated in industrial activities such as electrolytic aluminum, coal burning, steel processing and phosphate fertilizer production. These wastes can enter the environment through various channels and affect the safety of ecosystems and human health. In addition, the high background content of fluorine in the soil, coupled with the increasing use and emission of fluorine, will also lead to excessive fluorine content in the soil in some areas. Under the scouring effect of precipitation, these fluorides flow into rivers and lakes with sediment, gradually accumulate in sediments, and pose a serious threat to the quality of the water environment. Therefore, the environmental governance of water sources urgently needs to pay attention to this issue. Dredging, as an important measure to eliminate endogenous pollution and improve water environment quality, faces the challenge of fluorine pollution in sediments. If effective pollution remediation is not carried out, directly landfilling the contaminated sediment as hazardous waste is not only costly, but also difficult to find a suitable landfill site, which brings greater difficulties to environmental governance.

[0003] The leaching remediation technology is to inject a specific eluent into the medium, use gravity and hydraulic pressure head to push the eluent to penetrate the soil, thereby dissolving and separating the pollutants in it to achieve the purpose of remediation. This technology mainly has two ways to remove pollutants: one is to combine the pollutants with the eluent through chemical reactions, and remove them through reactions such as desorption, chelation, dissolution or fixation; the other is to directly remove the pollutants in the medium through physical flushing. Water, chemical solvents or gases can all be used as eluents and are considered to be fluids that can extract pollutants from the medium. Compared with other soil remediation technologies, leaching remediation technology has better removal efficiency and effect, can significantly reduce heavy metal pollution and effectively remove contaminated sites, so there is no need for long-term monitoring of the remediation area, becoming a convenient and efficient treatment method. However, at present, leaching technology is mainly used for the remediation of coarse-grained contaminated soils with high sand content and strong permeability, but for clay soils or bottom muds with poor permeability in rivers, lakes and reservoirs, the leaching remediation efficiency is low, especially for fluorine pollution. There are relatively few studies. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for strengthening the restoration of low-permeability fluorine-contaminated sludge by combining microbubbles with eluents. The method can treat fluorine-contaminated sludge with poor permeability in situ and achieve eluting and restoration of fluorine in the sludge. The method has high restoration efficiency and small environmental impact.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for repairing low-permeability fluorine-contaminated sludge, characterized by comprising the following steps:

[0007] S1, preparing an eluent: mixing three solutions of citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine, so that the concentrations of citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine in the solution are 0.1-0.5 mol / L, 0.01-0.1 mol / L and 0.01-0.1 mol / L, respectively;

[0008] S2, repairing fluorine-contaminated sludge: adding the eluent prepared in S1 to the fluorine-contaminated sludge, and continuously stirring in the elution stirring box for 1 to 2 hours, wherein the mass ratio of the fluorine-contaminated sludge to the eluent is 1:(10 to 30); during the elution process, using a pressurized air pump to pump air from under the porous disk at the bottom of the elution stirring box, using the formation of microbubbles to perform microbubble-elution combined enhanced repair on the eluted fluorine-contaminated sludge;

[0009] S3, separates the mud and water from the bottom mud repaired in S2 and completes leaching.

[0010] Preferably, the concentrations of citric acid, diethylenetriaminepentaacetic acid and cocamidopropyl betaine in S1 are 0.3 mol / L, 0.05 mol / L and 0.1 mol / L respectively.

[0011] Preferably, the volume ratio of the gas pumped into S2 to the mud-liquid mixture in the leaching and stirring tank is 1:(3-10). More preferably, the volume ratio of the gas pumped into S2 to the mud-liquid mixture in the leaching and stirring tank is 1:3.

[0012] Preferably, the pore size of the porous disk is 0.5 μm, and the diameter of the generated microbubbles ranges from 0.300 to 100 μm.

[0013] In S2, the mass ratio of fluorine-contaminated sludge to eluent is 1:20.

[0014] The fluorine-contaminated sludge is the sludge that has been cleaned, mechanically ground and passed through a 5-10 mm sieve. The fluorine-contaminated sludge is low-permeability clay, silty clay or silt.

[0015] Preferably, the stirring speed of the elution stirring box is 100-200 r / min, and the temperature is 20-40° C. The stirring speed of the elution stirring box is 200 r / min, the temperature is 25° C., and the stirring time is 2 h.

[0016] Compared with the existing methods, the present invention has the following advantages and beneficial effects:

[0017] 1. The present invention uses citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine as eluents, combined with microbubble technology for enhanced repair. For the water-soluble fluoride, exchangeable fluoride, iron-manganese-bound fluoride and organic-bound fluoride in the sediment, citric acid increases the solubility of sediment fluoride by lowering the pH of the sediment, and promotes the conversion from solid state to soluble state through ion exchange; diethylenetriaminepentaacetic acid complexes with water-soluble fluoride and exchangeable fluoride through chelation, further reducing the biological effectiveness of sediment fluoride, and at the same time promotes the conversion of iron-manganese-bound fluoride and organic-bound fluoride to water-soluble fluoride and exchangeable fluoride to a certain extent, effectively avoiding the re-adsorption of fluoride ions on the sediment surface, and further improving the elution efficiency; the combination of cocamidopropyl betaine and microbubbles can synergistically reduce the surface tension of sediment particles, reinforce each other with bubbles, improve the viscosity of sediment, enhance the permeability of eluent, enable it to more effectively contact and remove fluoride in sediment, promote the equilibrium reaction of the elution system to shift towards the release of fluoride ions, and achieve the purpose of enhanced elution and remediation.

[0018] 2. The addition of microbubbles in the present invention can promote the equilibrium reaction of the elution system to shift toward the direction of releasing fluoride ions, thereby improving the effectiveness of the eluent in sediment remediation, reducing the amount of eluent used, and reducing costs.

[0019] 3. In the present invention, the microbubbles also react with cocamidopropyl betaine to form surfactant microbubbles or colloidal gas foams with small volume and large specific surface area, which can effectively reduce the surface tension between the pollutants and the liquid phase, promote the adsorption of pollutants on the surface of the microbubbles or colloidal gas foams and transfer them to the gas phase, and ultimately achieve the purpose of enhancing the leaching efficiency of fluorine-contaminated sludge.

[0020] 3. The process of the present invention is simple, easy to operate, has a fast reaction speed, and a good elution effect. It can effectively overcome the problem of difficulty in eluting low-permeability sediments. It can be applied to the remediation of fluorine pollution in sediments of various texture types such as clay, silty clay, and silt, and can also be widely used in the elution remediation of fluorine-containing soils.

[0021] 3. The sludge after elution and repair by the method of the present invention will not cause secondary pollution when it is backfilled and utilized as a resource after being washed with clean water. Citric acid, diethylenetriaminepentaacetic acid and cocamidopropyl betaine are all biodegradable, environmentally friendly, and will not cause secondary pollution.

[0022] 4. The total fluorine content of fluorine-contaminated sludge repaired by this method can be reduced by more than 67.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the fluorine removal rate of the remediated contaminated sludge under different citric acid addition conditions;

[0024] Figure 2 is the fluorine removal rate of the remediated contaminated sludge under different addition amounts of diethylenetriaminepentaacetic acid;

[0025] Figure 3 is the fluorine removal rate of the remediated contaminated sludge under different addition amounts of cocamidopropyl betaine;

[0026] Figure 4 is the fluorine removal rate of the fluorine-contaminated sludge being repaired under different gas-liquid ratio conditions;

[0027] Figure 5 It is the fluorine removal rate of microbubbles combined with eluents to enhance the restoration of polluted sediments of different texture types. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the method of the present invention is described in detail below in conjunction with embodiments and drawings.

[0029] Example 1

[0030] A sediment sample was collected from a reservoir in Hebei Province. The sediment had a moisture content of 13.9%, a pH of 7.9, a silt texture, and a total fluorine content of 562 mg / kg.

[0031] The above fluorine-contaminated sludge was repaired under different citric acid addition conditions. The specific steps are as follows:

[0032] S1. Remove impurities from the fluorine-contaminated sludge, grind it mechanically, pass it through a 10mm sieve, and then divide it into 5 groups of equal quality.

[0033] S2, prepare 5 groups of eluent solutions, wherein the concentrations of citric acid in the 5 groups of solutions are 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.5mol / L and 1.0mol / L, respectively, the concentrations of diethylenetriaminepentaacetic acid in the 5 groups of solutions are all 0.05mol / L, and the concentrations of cocamidopropyl betaine in the 5 groups of solutions are all 0.1mol / L;

[0034] S3, add 5 groups of eluent solutions prepared in S2 to the 5 groups of fluorine-contaminated sludge obtained in S1, with a solid-liquid ratio of 1:20, and stir for 2 hours at 25°C and 200r / min. During the elution process, use a pressurized air pump to pump microbubbles (0.300-100μm) from the porous disk at the bottom of the stirring box, with a gas-liquid ratio of 1:3, and perform microbubble-elution combined enhanced remediation on the fluorine-contaminated sludge saturated with elution;

[0035] S4. Separate the mud and water from the five groups of sediments after the microbubble-elution combined enhanced restoration to obtain five groups of restored fluorine-contaminated sediments.

[0036] The five groups of repaired fluorine-contaminated sludge were dried separately and then the total fluoride content of the repaired sludge was determined according to the method specified in the "Determination of Fluoride in Solid Waste by Alkali Fusion-Ion Selective Electrode Method" (HJ 999-2018). The results are as follows Figure 1 and Figure 5 (silt) shown.

[0037] As can be seen from the figure, the amount of citric acid added has a great influence on the leaching effect of fluoride-contaminated sludge. Taking into account the fluoride removal rate and the cost of the elution agent, when the amount of citric acid added is 0.3 mol / L, the fluoride removal rate of the repaired sludge is the best, and the total fluoride content of the contaminated sludge is reduced from the original 562 mg / kg to 69.7 mg / kg, with a removal rate of up to 87.6%.

[0038] Example 2

[0039] A sediment sample was collected from a river in Tianjin. The sediment had a moisture content of 13.8%, a pH of 8.1, a clay texture, and a total fluorine content of 775 mg / kg.

[0040] The above fluorine-contaminated sludge was repaired under different diethylenetriaminepentaacetic acid addition conditions. The specific steps are as follows:

[0041] S1. Remove impurities from the fluorine-contaminated sludge, grind it mechanically, and pass it through a 10 mm sieve, and divide it into 5 groups of equal quality;

[0042] S2, prepare 5 groups of eluent solutions, wherein the concentration of citric acid in the 5 groups of solutions is 0.3 mol / L, the concentration of diethylenetriaminepentaacetic acid in the 5 groups of solutions is 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, respectively, and the concentration of cocamidopropyl betaine in the 5 groups of solutions is 0.1 mol / L;

[0043] S3, add 5 groups of eluent solutions prepared in S2 to the 5 groups of fluorine-contaminated sludge obtained in S1, with a solid-liquid ratio of 1:20, and stir continuously for 2 hours at 25°C and 200r / min; during the elution process, use a pressurized air pump to pump microbubbles from the porous disk at the bottom of the stirring box, with a gas-liquid ratio of 1:3, and perform microbubble-elution combined enhanced remediation on the eluted saturated fluorine-contaminated sludge;

[0044] S4. Separate the mud and water from the five groups of sediments after the microbubble-elution combined enhanced restoration to obtain five groups of restored fluorine-contaminated sediments.

[0045] The five groups of repaired fluorine-contaminated sludge were dried separately and then the total fluoride content of the repaired sludge was determined according to the method specified in the "Determination of Fluoride in Solid Waste by Alkali Fusion-Ion Selective Electrode Method" (HJ 999-2018). The results are as follows Figure 2 and Figure 5 (Clay) shown.

[0046] As can be seen from the figure, the addition amount of diethylenetriaminepentaacetic acid has a great influence on the elution effect of fluoride-contaminated sludge. When the addition amount of diethylenetriaminepentaacetic acid is 0.05 mol / L, the fluoride removal rate of the restored sludge reaches the best, and the total fluoride content of the contaminated sludge is reduced from the original 775 mg / kg to 251.9 mg / kg, and the removal rate is as high as 67.5%.

[0047] Example 3

[0048] A sediment sample was collected from a reservoir in Shanxi Province. The sediment had a moisture content of 20.1%, a pH of 7.8, a texture type of silty clay, and a total fluorine content of 866 mg / kg.

[0049] Under the conditions of different addition amounts of cocamidopropyl betaine, the fluorine-contaminated sludge was repaired. The specific steps are as follows:

[0050] S1. Remove impurities from the fluorine-contaminated sludge, grind it mechanically, and pass it through a 10mm sieve, and divide it into 5 groups of equal mass;

[0051] S2, prepare 5 groups of eluent solutions, wherein the concentration of citric acid in the 5 groups of solutions is 0.3 mol / L, the concentration of diethylenetriaminepentaacetic acid in the 5 groups of solutions is 0.05 mol / L, and the concentration of cocamidopropyl betaine in the 5 groups of solutions is 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, respectively;

[0052] S3. Add the eluent solution prepared in S2 to the five groups of fluorine-contaminated sludges obtained in S1 respectively, with a solid-liquid ratio of 1:20, and continue stirring at 25°C and 200 r / min for 2 h. During the elution process, use a pressurized air pump to pump microbubbles into the porous disk at the bottom of the stirring box, with a gas-liquid ratio of 1:3, and perform microbubble-elution combined enhanced remediation on the eluted saturated fluorine-contaminated sludge.

[0053] S4. Separate the mud and water from the five groups of sediments after the microbubble-elution combined enhanced restoration to obtain five groups of restored fluorine-contaminated sediments.

[0054] After drying the five groups of repaired fluorine-contaminated sludge, the total fluorine content of the repaired sludge was determined according to the method specified in the "Determination of Fluoride in Solid Waste by Alkali Fusion-Ion Selective Electrode Method" (HJ 999-2018). The results are as follows: Figure 3 shown.

[0055] Depend on Figure 3It can be seen that the addition amount of cocamidopropyl betaine has a great influence on the elution effect of fluoride-contaminated sludge. When the addition amount of cocamidopropyl betaine is 0.1 mol / L, the fluoride removal rate of the sludge after repair is the best. The total fluoride content of the contaminated sludge is reduced from the original 886 mg / kg to 185.3 mg / kg, and the removal rate is as high as 78.6%.

[0056] Example 4

[0057] Taking the sediment sample of a reservoir in Shanxi Province in Example 3 as an example, the moisture content of the sediment is 20.1%, the pH is 7.8, the texture type is silty clay, and the total fluorine content is 866 mg / kg.

[0058] The specific steps for remediation of fluorine-contaminated sludge under different gas-liquid ratio conditions are as follows:

[0059] S1. Remove impurities from the fluorine-contaminated sludge, grind it mechanically, and pass it through a 10mm sieve, and evenly divide it into 6 groups according to quality;

[0060] S2, prepare 6 groups of eluent solutions, wherein the concentration of citric acid in the 6 groups of solutions is 0.3 mol / L, the concentration of diethylenetriaminepentaacetic acid in the 6 groups of solutions is 0.05 mol / L, and the concentration of cocamidopropyl betaine in the 6 groups of solutions is 0.1 mol / L;

[0061] S3. To the six groups of fluorine-contaminated sludges obtained in S1, the eluent solutions prepared in S2 were added respectively, with a solid-liquid ratio of 1:20, and the mixtures were stirred continuously at 25°C and 200 r / min for 2 h. During the elution process, a pressurized air pump was used to pump microbubbles into the saturated fluorine-contaminated sludge from the porous disk at the bottom of the stirring tank. The gas-liquid ratios of the six elution systems (the volume ratio of the pumped gas to the mud-liquid mixture in the elution stirring tank) were 0:9, 1:9, 3:9, 5:9, 7:9, and 9:9, respectively. The eluted saturated fluorine-contaminated sludge was subjected to microbubble-elution combined enhanced remediation.

[0062] S5. Separate the sludge from the water after the restoration by the combined microbubble-elution enhanced method to obtain 6 groups of restored fluorine-contaminated sludge.

[0063] After drying the six groups of repaired fluorine-contaminated sludge, the total fluorine content of the repaired sludge was determined according to the method specified in the "Determination of Fluoride in Solid Waste by Alkali Fusion-Ion Selective Electrode Method" (HJ 999-2018). The results are as follows: Figure 4 and Figure 5 (Silty clay) shown.

[0064] As can be seen from the figure, the gas-liquid ratio of the elution system has a great influence on the elution effect of fluoride-contaminated sludge. When the gas-liquid ratio is 1:3 (i.e. 3:9 in the figure), the fluoride removal rate of the sludge after repair reaches the best, and the total fluoride content of the contaminated sludge is reduced from the original 886 mg / kg to 169.74 mg / kg, with a removal rate of up to 80.4%.

Claims

1. A method for repairing low-permeability fluorine-contaminated sludge, characterized in that The following steps are involved: S1, preparing an eluent: mixing three solutions of citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine, so that the concentrations of citric acid, diethylenetriamine pentaacetic acid and cocamidopropyl betaine in the solution are 0.1-0.5 mol / L, 0.01-0.1 mol / L and 0.01-0.1 mol / L, respectively; S2, repairing fluorine-contaminated sludge: adding the eluent prepared in S1 to the fluorine-contaminated sludge, and continuously stirring in the elution stirring box for 1 to 2 hours, wherein the mass ratio of the fluorine-contaminated sludge to the eluent is 1:(10 to 30); during the elution process, using a pressurized air pump to pump air from under the porous disk at the bottom of the elution stirring box, using the formation of microbubbles to perform microbubble-elution combined enhanced repair on the eluted fluorine-contaminated sludge; S3, separates the mud and water from the bottom mud repaired in S2 and completes leaching.

2. The repair method according to claim 1, characterized in that: In S1, the concentrations of citric acid, diethylenetriaminepentaacetic acid and cocamidopropyl betaine are 0.3 mol / L, 0.05 mol / L and 0.1 mol / L respectively.

3. The repair method according to claim 1, characterized in that: In S2, the volume ratio of the pumped gas to the mud-liquid mixture in the leaching mixing tank is 1:(3-10).

4. The repair method according to claim 3, characterized in that: The volume ratio of the pumped gas to the mud-liquid mixture in the leaching mixing box is 1:

3.

5. The repair method according to claim 1, characterized in that: The pore size of the porous disc is 0.5 μm, and the diameter of the generated microbubbles ranges from 0.300 to 100 μm.

6. The repair method according to claim 1, characterized in that: In S2, the mass ratio of fluorine-contaminated sludge to eluent is 1:

20.

7. The repair method according to claim 1, characterized in that: The fluorine-contaminated sludge is the sludge that has been cleaned of impurities, mechanically ground and sieved through a 5-10 mm sieve.

8. The repair method according to claim 7, characterized in that: The fluorine-contaminated sludge is low-permeability clay, silty clay or silt.

9. The repair method according to claim 1, characterized in that: The stirring speed of the elution stirring box is 100-200 r / min, and the temperature is 20-40°C.

10. The repair method according to claim 9, characterized in that: The stirring speed of the elution stirring box is 200 r / min, the temperature is 25° C., and the stirring time is 2 h.

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