Repairing agent for repairing DNAPL pollution based on chemical oxidation and preparation method

Abstract

The invention discloses a repairing agent for repairing DNAPL pollution based on chemical oxidation and a preparation method, the repairing agent comprises 32.5-49.5 wt% of an oxidizing agent and 50.5-67.5 wt% of a composite eluting agent, and the composite eluting agent is composed of 12.5-24.5 wt% of lauryl sodium sulfate, 21.5-32.9 wt% of plant polyenol polyoxyethylene ether, 6-18 wt% of polyethylene glycol and 24.6-60 wt% of deionized water. According to the method, the DNAPL pollutants existing in the soil are eluted and separated out through the composite eluting agent, then the separated DNAPL pollutants are oxidized through the oxidizing agent, and the problem that when the DNAPL pollutants exist in areas, such as a fracture layer or a clay layer, where the oxidizing agent cannot reach easily, or the oxidizing agent cannot be rapidly, completely and uniformly diffused due to soil or stones, the DNAPL pollutants cannot be oxidized through the oxidizing agent is solved. And the repair period of the in-situ chemical oxidation technology is greatly prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of environmental restoration, and in particular to a repair agent for repairing DNAPL pollution based on chemical oxidation and a preparation method thereof. Background Art

[0002] DNAPL is a typical type of organic pollution in groundwater. Its main components are mostly organic substances with a density greater than that of water and are not easily soluble in water. As an important industrial raw material, DNAPL is widely used in agriculture, fuel and medicine. Accidents and unreasonable disposal during production, transportation, storage and use will cause DNAPL to enter the soil. Under the action of gravity, it will continue to infiltrate into extremely small pores or penetrate clay layers. When it accumulates to a certain amount, it can form a DNAPL pollution pool. Once DNAPL enters the underground environment, due to the very slow mass transfer process of its main components from the pure phase to the dissolved phase, DNAPL can slowly and continuously release its pollutants into the underground environment; in addition, due to the low biodegradability of DNAPL, its natural attenuation in the underground environment is slow, so the remediation of DNAPL pollution sources is also called "eternal remediation."

[0003] However, during the current DNAPL pollution remediation, when DNAPL pollutants exist in areas that are difficult for oxidants to reach, such as fracture layers or clay layers, or when soil or stones prevent the oxidants from spreading quickly, completely and evenly, the remediation cycle of the in-situ chemical oxidation technology will be greatly extended. We can leach out the DNAPL pollutants in the soil through leaching, and then use oxidants to oxidize the precipitated DNAPL pollutants, which can improve the remediation effect of DNAPL pollution. The effect of the use of oxidants is particularly important. Therefore, a new type of remediation agent is needed to solve the above problems. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a repair agent for repairing DNAPL pollution based on chemical oxidation and a preparation method thereof.

[0005] The technical solution of the present invention is: a repair agent for repairing DNAPL pollution based on chemical oxidation, comprising 32.5-49.5wt% oxidant and 50.5-67.5wt% composite eluent,

[0006] The composite eluent is composed of 12.5-24.5wt% sodium dodecyl sulfate, 21.5-32.9wt% plant polyphenol polyoxyethylene ether (plant type polyphenol NSF), 6-18wt% polyethylene glycol and 24.6-60wt% deionized water.

[0007] In one embodiment of the present invention, the oxidant is selected from any one of potassium permanganate, hydrogen peroxide or sodium persulfate.

[0008] Description: Oxidants can react chemically with DNAPL pollutants, oxidizing and decomposing them into non-toxic or low-toxic small molecules, or even completely mineralizing them into carbon dioxide and water. This decomposition and transformation process can significantly reduce the toxicity of pollutants and reduce their harm to the environment and human body. By adding the above-mentioned oxidants, the degradation process of DNAPL pollutants can be accelerated and the remediation efficiency can be improved, especially in difficult-to-remediate areas such as low-permeability aquifers, which can more effectively remove pollutants and reduce remediation costs and time.

[0009] The present invention also provides a method for preparing a repair agent when the oxidant is any one of potassium permanganate, hydrogen peroxide or sodium persulfate, wherein sodium lauryl sulfate, plant polyphenol polyoxyethylene ether and polyethylene glycol are sequentially added to deionized water and mixed to obtain a composite eluent, and the oxidant and the composite eluent are stored separately.

[0010] Description: The above method can be used to prepare a composite eluent, which can be stored separately to avoid being affected by the oxidant or the composite eluent. When in use, the respective effects of the composite eluent and the oxidant are maintained to achieve the expected effect of DNAPL pollution control.

[0011] In another embodiment of the present invention, the oxidant is a coated oxidant, wherein the coated oxidant is obtained by using stearic acid as a shell material to wrap an oxidizing core material, and the oxidizing core material is any one of potassium permanganate and sodium persulfate.

[0012] Description: The above-mentioned oxidant design can control the non-selective consumption of the repair agent, thereby improving the removal efficiency of DNAPL pollutants and solving the problem of poor long-term effectiveness of DNAPL pollution. In addition, by using a coated oxidant, it can be pre-mixed with a composite eluent, thereby optimizing the use process of the repair agent. There is no need to add composite eluents and oxidants in steps, which simplifies the operation process and improves the convenience of using the repair agent.

[0013] Furthermore, the preparation method of the coated oxidant is:

[0014] 1) Stearic acid and cyclohexane are mixed and stirred at a ratio of 100-200 g:1 L, and heated in a water bath to 73-78° C., and after the stearic acid is completely dissolved, a mixed base liquid is obtained;

[0015] 2) adding the oxidized core material to the mixed base liquid and ultrasonically stirring for 10 to 20 minutes to uniformly disperse the oxidized core material in the mixed base liquid, wherein the oxidized core material and cyclohexane are added in a ratio of 50 to 100 g: 1 L;

[0016] 3) adding polyethylene glycol gradually to the mixed base liquid, and at the same time lowering the water bath temperature to room temperature at a cooling rate of T°C / min to obtain a precipitate, wherein the single addition amount of the polyethylene glycol is Mg / min;

[0017] 4) Then, the precipitate is placed in a 40-50° C. oven for curing for 3-5 hours, during which the precipitate is stirred for 3-5 minutes every 20-40 minutes, and a composite liquid accounting for 2-5% of the mass of the precipitate is sprinkled, and finally crushed and sieved to obtain a coated oxidant;

[0018] Wherein, the temperature reduction amplitude ΔT of the mixed base liquid is 48-53°C, and the temperature reduction rate T∈[2,5], unit: °C / min;

[0019] Polyethylene glycol and cyclohexane are added in a ratio of 30-50 g:1 L. The total amount of polyethylene glycol added is M 0 is 30 to 50 g, and M satisfies the following formula:

[0020]

[0021] Wherein, M is the single addition amount of polyethylene glycol, unit: g / min.

[0022] Description: The above method can effectively prepare an oxidant with a sustained-release function. Since the cooling rate and the polyethylene glycol addition rate affect the precipitation rate of stearic acid, the stearic acid cannot be evenly dispersed around the oxidized core material, thereby affecting the use effect of some coated oxidants. Therefore, by optimizing the polyethylene glycol addition rate and the cooling rate, a coated oxidant with better performance can be obtained.

[0023] At the same time, by using the composite liquid to spray at a fixed time and in a fixed quantity during the solidification of the precipitate, the structure of the coated oxidant can be strengthened by using the composite liquid and coordinating the temperature difference change, which can further improve the use effect of the coated oxidant and thus improve the use effect of the repair agent in the treatment of DNAPL pollution.

[0024] Furthermore, since the cooling rate and the polyethylene glycol addition rate affect the precipitation rate of stearic acid, the above formula provides guidance for the single addition amount of polyethylene glycol. Under this method, stearic acid can be evenly dispersed around the oxidized core material, thereby improving the use effect of the coated oxidant and obtaining a coated oxidant with better performance.

[0025] Furthermore, the composite liquid includes 2-7 wt % of carboxypropyl methylcellulose, 5-18 wt % of acetic acid and 75-93 wt % of deionized water, and the temperature of the composite liquid is 17-20° C.

[0026] Description: By adding carboxypropyl methylcellulose and acetic acid into deionized water in a certain proportion, during the curing period of the coated oxidant, low temperature can significantly improve the use effect of the prepared coated oxidant, thereby improving the effect of the repair agent on DNAPL pollution control.

[0027] The present invention also provides a method for preparing a repair agent in which the oxidant is a coated oxidant, wherein the coated oxidant is a repair agent in which stearic acid is used as a shell material to wrap an oxidized core material, comprising the following steps:

[0028] S1. Add sodium lauryl sulfate, plant polyphenol polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite eluent for later use;

[0029] S2. The coated oxidant and the composite eluent are mixed in a ratio of 32.5-49.5 wt % of the coated oxidant and 50.5-67.5 wt % of the composite eluent to obtain a repair agent for repairing DNAPL pollution.

[0030] Description: The above method can be used to obtain a mixed repair agent. By premixing the coated oxidant and the composite eluent, the use process of the repair agent is optimized. There is no need to add the composite eluent and oxidant step by step, which simplifies the operation process and improves the convenience of using the repair agent.

[0031] Furthermore, the repair agent is prepared and used immediately, and the coated oxidant and the composite eluent are used within 48 hours after being compounded.

[0032] Note: In order to prevent the coated oxidant from being immersed in the composite eluent for a long time, the above method can effectively avoid this problem and avoid affecting the sustained release effect of the coated oxidant, thereby ensuring the use effect of the repair agent.

[0033] The beneficial effects of the present invention are:

[0034] (1) The repair agent of the present invention uses the composite eluent to leach out the DNAPL pollutants present in the soil, and then uses the oxidant to oxidize the precipitated DNAPL pollutants, thereby solving the problem in the prior art that the repair cycle of the in-situ chemical oxidation technology will be greatly prolonged when the DNAPL pollutants are present in areas such as fracture layers or clay layers that are difficult for oxidants to reach, or when the soil or stones prevent the oxidants from spreading quickly, completely and evenly.

[0035] (2) The present invention can effectively simplify the use steps of the repair agent by using a coated oxidant, without the need to add a composite eluent and an oxidant in steps, and the oxidative activity is long-lasting, which can effectively control the release of the oxidized core material, reduce the non-selective consumption of the oxidant, and improve the removal efficiency of DNAPL pollutants.

[0036] (3) The present invention can improve the use effect of the coated oxidant by optimizing the preparation method of the coated oxidant, solve the problem that stearic acid cannot be evenly dispersed around the oxidizing core material, affecting the use effect of part of the coated oxidant, thereby preparing a coated oxidant with better use performance. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with specific implementation methods to better reflect the advantages of the present invention.

[0038] Example 1: A repair agent for repairing DNAPL pollution based on chemical oxidation, comprising 45.5wt% oxidant and 54.5wt% composite eluent. It should be noted that the amount of the composite eluent is adjusted according to the DNAPL pollution situation.

[0039] The composite eluent is composed of 18.7 wt% sodium dodecyl sulfate, 27.6 wt% plant polyphenol polyoxyethylene ether (plant polyphenol NSF), 14.5 wt% polyethylene glycol and 39.2 wt% deionized water. The oxidant is selected from commercially available potassium permanganate.

[0040] The preparation method of the above-mentioned repair agent is as follows: sodium dodecyl sulfate, plant polyphenol polyoxyethylene ether, and polyethylene glycol are added to deionized water in sequence and mixed to obtain a composite eluent, and the oxidant and the composite eluent are stored separately. When treating DNAPL pollution, the DNAPL pollutants present in the soil are eluted and precipitated by the eluent, and then the oxidant is used to oxidize the precipitated DNAPL pollutants.

[0041] Example 2: This example is different from Example 1 in that the repair agent includes 32.5 wt % of an oxidant and 67.5 wt % of a composite eluent.

[0042] Example 3: This example is different from Example 1 in that the repair agent includes 49.5 wt % of an oxidant and 50.5 wt % of a composite eluent.

[0043] Example 4: This example is different from Example 1 in that the composite eluent is composed of 12.5wt% sodium dodecyl sulfate, 21.5wt% plant polyphenol polyoxyethylene ether (plant polyphenol NSF), 6wt% polyethylene glycol and 60wt% deionized water.

[0044] Example 5: This example is different from Example 1 in that the composite eluent is composed of 24.5wt% sodium dodecyl sulfate, 32.9wt% plant polyphenol polyoxyethylene ether (plant polyphenol NSF), 18wt% polyethylene glycol and 24.6wt% deionized water.

[0045] Simulate DNAPL pollution to test, set up multiple groups of 3m 2 The DNAPL contaminated areas were identified, and the DNAPL content in each DNAPL contaminated area was basically kept consistent by DNAPL injection. The DNAPL contaminated areas were then repaired for 90 days using the above method. The DNAPL contaminated areas before and after the repair were compared to calculate the DNAPL removal rate. The results are shown in Table 1 below:

[0046] Table 1 DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation

[0047]

[0048] At the same time, a control group treated with only an oxidant was set up to compare the DNAPL contaminated area before and after 90 days of repair, and the removal rate of DNAPL was calculated. The results are shown in Table 2 below:

[0049] Table 2 DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation

[0050]

[0051] From the results in Table 1 and Table 2 above, it can be seen that after using the repair method of composite eluent combined with oxidant, the DNAPL removal rate is significantly better than the control. At the same time, when using different doses of oxidant and composite eluent, there are certain differences in the treatment of DNAPL contaminated areas. The specific analysis is as follows:

[0052] 1) For Example 2, after the amount of oxidant was reduced and the amount of composite eluent was increased, the DNAPL removal rate decreased. This may be because even if the elution was sufficient, the amount of oxidant was too small, which affected the removal effect of DNAPL. For Example 3, after the amount of oxidant was increased and the amount of composite eluent was reduced, the DNAPL removal rate also decreased. This may be due to insufficient elution, the presence of DNAPL pollutants in areas such as fracture layers or clay layers that are difficult for oxidants to reach, or the soil or stones prevented the oxidant from quickly and completely spreading evenly, so even if the amount of oxidant was too much, the DNAPL removal rate could not be improved;

[0053] 2) For Example 4 and Example 5, after the composition of the composite eluent was changed, the DNAPL removal rates decreased. It can be seen that the composite eluent of Example 1 has the best elution effect.

[0054] Example 6: This example is different from Example 1 in that the oxidant is commercially available hydrogen peroxide.

[0055] Example 7: This example is different from Example 1 in that the oxidant is commercially available sodium persulfate.

[0056] Example 8: This example is different from Example 1 in that the oxidant is a coated oxidant, which is obtained by using stearic acid as a shell material to wrap an oxidizing core material, and the oxidizing core material is potassium permanganate. The preparation method of the coated oxidant is:

[0057] 1) Stearic acid and cyclohexane were mixed and stirred at a ratio of 160 g:1 L, and heated in a water bath to 76° C., and after the stearic acid was completely dissolved, a mixed base liquid was obtained;

[0058] 2) adding the oxidized core material to the mixed base liquid and ultrasonically stirring for 15 minutes at a stirring speed of 300 r / min to uniformly disperse the oxidized core material in the mixed base liquid, wherein the oxidized core material and cyclohexane are added at a ratio of 80 g:1 L;

[0059] 3) adding polyethylene glycol gradually to the mixed base liquid, and at the same time lowering the water bath temperature to room temperature (25° C.) at a cooling rate of T° C. / min to obtain a precipitate, wherein the single addition amount of the polyethylene glycol is Mg / min;

[0060] 4) The precipitate was then placed in a 45° C. oven for curing for 4 h, during which the precipitate was stirred for 4 min every 30 min at a stirring speed of 150 r / min, and a composite liquid accounting for 4.5% of the mass of the precipitate was sprinkled, and finally crushed and sieved to obtain a coated oxidant.

[0061] The composite liquid includes 5 wt % carboxypropyl methylcellulose, 16 wt % acetic acid and 79 wt % deionized water, and the temperature of the composite liquid is 18° C.

[0062] The temperature reduction amplitude ΔT of the mixed base liquid is 51°C, and the temperature reduction rate T∈4°C / min;

[0063] Polyethylene glycol and cyclohexane are added in a ratio of 40 g:1 L. The total amount of polyethylene glycol added is M 0 is 40g, and M satisfies the following formula:

[0064]

[0065] Wherein, M is the single addition amount of polyethylene glycol, unit: g / min;

[0066] It is calculated that M is 3.14 g / min. It should be noted that the integer is used.

[0067] The preparation method of the above-mentioned repair agent comprises the following steps:

[0068] S1. Add sodium lauryl sulfate, plant polyphenol polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite eluent for later use;

[0069] S2. Mix the coated oxidant and the composite eluent in a ratio of 45.5 wt % oxidant to 54.5 wt % composite eluent to obtain a repair agent for repairing DNAPL pollution.

[0070] It should be noted that the repair agent is prepared and used immediately, and the coated oxidant and the composite eluent are used within 48 hours after being compounded. The repair agent of the present invention can be used directly as a liquid repair agent by spraying, landfilling, stirring, etc.

[0071] Example 9: This example is different from Example 8 in that stearic acid and cyclohexane are mixed and stirred at a ratio of 100 g:1 L, the oxidized core material and cyclohexane are added at a ratio of 100 g:1 L, and the polyethylene glycol and cyclohexane are added at a ratio of 50 g:1 L.

[0072] Example 10: This example is different from Example 8 in that stearic acid and cyclohexane are mixed and stirred at a ratio of 200 g:1 L, the oxidized core material and cyclohexane are added at a ratio of 50 g:1 L, and the polyethylene glycol and cyclohexane are added at a ratio of 30 g:1 L.

[0073] Example 11: This example is different from Example 8 in that the water bath is heated to 73°C.

[0074] Example 12: This example is different from Example 8 in that the water bath is heated to 78°C.

[0075] Example 13: This example is different from Example 8 in that the oxidized core material is added to the mixed base liquid and ultrasonically stirred for 10 minutes at a stirring speed of 200 r / min.

[0076] Example 14: This example is different from Example 8 in that the oxidized core material is added to the mixed base liquid and ultrasonically stirred for 20 minutes at a stirring speed of 400 r / min.

[0077] Example 15: This example is different from Example 8 in that polyethylene glycol is added gradually to the mixed base liquid, the single addition amount of polyethylene glycol is M g / min, and the water bath temperature is lowered to room temperature at a cooling rate of 2°C / min, and M satisfies the following formula:

[0078]

[0079] Wherein, M is the single addition amount of polyethylene glycol, unit: g / min;

[0080] It was calculated that M was 1.57 g / min.

[0081] Example 16: This example is different from Example 8 in that polyethylene glycol is added gradually to the mixed base liquid, the single addition amount of polyethylene glycol is M g / min, and the water bath temperature is lowered to room temperature at a cooling rate of 5°C / min, and M satisfies the following formula:

[0082]

[0083] Wherein, M is the single addition amount of polyethylene glycol, unit: g / min;

[0084] It was calculated that M was 3.93 g / min.

[0085] Example 17: This example is different from Example 8 in that the precipitate is placed in a 40°C oven for curing for 5 hours, during which the precipitate is stirred for 3 minutes every 20 minutes and sprinkled with a composite liquid accounting for 5% of the mass of the precipitate.

[0086] Example 18: This example is different from Example 8 in that the precipitate is placed in a 50°C oven for curing for 3 hours, during which the precipitate is stirred for 5 minutes every 40 minutes and sprinkled with a composite liquid accounting for 2% of the mass of the precipitate.

[0087] Example 19: This example is different from Example 8 in that the composite liquid includes 2 wt % carboxypropyl methylcellulose, 5 wt % acetic acid and 93 wt % deionized water, and the temperature of the composite liquid is 17°C.

[0088] Example 20: This example is different from Example 8 in that the composite liquid includes 7 wt % carboxypropyl methylcellulose, 18 wt % acetic acid and 75 wt % deionized water, and the temperature of the composite liquid is 20°C.

[0089] In order to further verify the use effect of each repair agent, the above method is now used to repair the DNAPL contaminated area for 90 days using the repair agents of each embodiment. The DNAPL contaminated area before and after 90 days of repair is compared to calculate the removal rate of DNAPL. The results are shown in Table 3 below:

[0090] Table 3 DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation

[0091]

[0092] It can be seen from the results in Table 3 above that after using the composite eluent combined with the coated oxidant for remediation, the DNAPL removal rate is significantly better than that in Example 1. However, when using the coated oxidant and the composite eluent, there are certain differences in the treatment of the DNAPL contaminated area. The specific analysis is as follows:

[0093] 1) For Example 9, after increasing the proportion of the oxidized core material relative to stearic acid, the DNAPL removal rate decreased. This may be because the oxidized core material was not completely surrounded by stearic acid, which affected the sustained release performance of the prepared product. For Example 10, after reducing the proportion of the oxidized core material relative to stearic acid, the DNAPL removal rate also decreased. This may be because the proportion of the oxidized core material contained in the coated oxidant was too small, which affected the amount and effect of the oxidant in disguise. Therefore, the ratio of the oxidized core material to stearic acid in Example 8 is relatively optimal, and the effect is better in actual DNAPL pollution control;

[0094] 2) For Example 11 and Example 12, after changing the water bath temperature, the DNAPL removal rate of Example 11 decreased to a certain extent, while Example 12 was basically the same as Example 8. This may be because the low temperature affected the dispersion and dissolution effect of the mixed system, and Example 12 required more heat energy to reach the temperature value. Therefore, the comprehensive use effect of Example 8 was relatively better;

[0095] 3) For Example 13 and Example 14, after changing the ultrasonic stirring time and stirring speed, the DNAPL removal rate of Example 13 decreased to a certain extent, while Example 14 was basically the same as Example 8. This may be because the mixed system was already uniformly dispersed under the ultrasonic stirring parameters of Example 8, and the degree of dispersion could not be further enhanced after further increasing the ultrasonic stirring time and stirring speed. At the same time, Example 14 required more energy to achieve the parameters. Therefore, the comprehensive use effect of Example 8 was relatively better.

[0096] 4) For Example 15 and Example 16, after calculating the M value by the formula of the present invention, a relatively stable coated oxidant use effect can be achieved according to different cooling rates. Among them, there are slight differences between Example 15 and Example 16 compared with Example 8, but the overall time consumption of Example 15 is longer, while the overall time consumption of Example 16 is shorter. Therefore, the corresponding selection can be made according to the actual production situation.

[0097] 5) For Example 17 and Example 18, after changing the parameters of the curing treatment, the DNAPL removal rates decreased to a certain extent. This may be because in Example 17, the use of too much composite liquid affected the curing effect of the precipitate, thereby affecting the sustained release performance of the coated oxidant, and the use of too little composite liquid affected the effect of the composite liquid, thereby affecting the performance of the coated oxidant. Therefore, the parameters of the curing treatment and the usage of the composite liquid in Example 8 are relatively optimal, and the use effect is better in the actual DNAPL pollution control;

[0098] 6) For Example 19 and Example 20, after changing the composition of the composite liquid, the DNAPL removal rates decreased. It can be seen that the composite liquid of Example 8 has the best effect in the solidification treatment.

[0099] At the same time, in order to further verify the effect of the composite liquid, a composite liquid (control 1) using only carboxypropyl methylcellulose and deionized water (supplement) was set, a composite liquid (control 2) using only acetic acid and deionized water (supplement), and a composite liquid (control 3) with the same combination as Example 8 but at the same temperature were set, and the DNAPL contaminated area before and after 90 days of repair was compared to calculate the removal rate of DNAPL. The results are shown in Table 2 below:

[0100] Table 4 DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation

[0101]

[0102] It can be seen from the results in Table 4 above that after using different composite liquids, the DNAPL removal rate decreased to a certain extent. It can be seen that the composite liquid composed of carboxypropyl methylcellulose and acetic acid added to deionized water in proportion can enhance the material properties of the coated oxidant, thereby improving the treatment effect of the repair agent in DNAPL; and after eliminating the temperature difference between the composite liquid and the precipitate, the use effect of the prepared coated oxidant also decreased significantly. Therefore, through the reasonable combination of the composite liquid and the temperature difference change, the use effect of the coated oxidant can be further improved, thereby improving the use effect of the repair agent in DNAPL pollution control.

Claims

1. A repair agent for repairing DNAPL contamination based on chemical oxidation, characterized in that: It includes 32.5-49.5wt% oxidant and 50.5-67.5wt% composite eluent, The composite eluent is composed of 12.5-24.5wt% sodium dodecyl sulfate, 21.5-32.9wt% plant polyphenol polyoxyethylene ether, 6-18wt% polyethylene glycol and 24.6-60wt% deionized water.

2. A repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 1, characterized in that: The oxidant is selected from any one of potassium permanganate, hydrogen peroxide or sodium persulfate.

3. The method for preparing a repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 2, characterized in that: Sodium dodecyl sulfate, plant polyphenol polyoxyethylene ether and polyethylene glycol are sequentially added into deionized water and mixed evenly to obtain a composite eluent, and the oxidant and the composite eluent are stored separately.

4. A repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 1, characterized in that: The oxidant is a coated oxidant, which is obtained by using stearic acid as a shell material to wrap an oxidizing core material, and the oxidizing core material is any one of potassium permanganate and sodium persulfate.

5. The method for preparing a repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 4, characterized in that: The preparation method of the coated oxidant is: 1) Stearic acid and cyclohexane are mixed and stirred at a ratio of 100-200 g:1 L, and heated in a water bath to 73-78° C., and after the stearic acid is completely dissolved, a mixed base liquid is obtained; 2) adding the oxidized core material to the mixed base liquid and ultrasonically stirring for 10 to 20 minutes to uniformly disperse the oxidized core material in the mixed base liquid, wherein the oxidized core material and cyclohexane are added in a ratio of 50 to 100 g: 1 L; 3) adding polyethylene glycol gradually to the mixed base liquid, and at the same time lowering the water bath temperature to room temperature at a cooling rate of T°C / min to obtain a precipitate, wherein the single addition amount of the polyethylene glycol is Mg / min; 4) Then, the precipitate is placed in a 40-50° C. oven for curing for 3-5 hours, during which the precipitate is stirred for 3-5 minutes every 20-40 minutes, and a composite liquid accounting for 2-5% of the mass of the precipitate is sprinkled, and finally crushed and sieved to obtain a coated oxidant; Wherein, the temperature reduction amplitude ΔT of the mixed base liquid is 48-53°C, and the temperature reduction rate T∈[2,5], unit: °C / min; Polyethylene glycol and cyclohexane are added in a ratio of 30-50 g:1 L, and the total amount of polyethylene glycol added M0 is 30-50 g, where M satisfies the following formula: Wherein, M is the single addition amount of polyethylene glycol, unit: g / min.

6. The method for preparing a repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 5, characterized in that: The composite liquid comprises 2-7 wt % of carboxypropyl methylcellulose, 5-18 wt % of acetic acid and 75-93 wt % of deionized water, and the temperature of the composite liquid is 17-20° C.

7. A method for preparing a repair agent for repairing DNAPL contamination based on chemical oxidation according to any one of claims 4 to 6, characterized in that: The following steps are involved: S1. Add sodium lauryl sulfate, plant polyphenol polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite eluent for later use; S2. The coated oxidant and the composite eluent are mixed in a ratio of 32.5-49.5 wt % of the coated oxidant and 50.5-67.5 wt % of the composite eluent to obtain a repair agent for repairing DNAPL pollution.

8. A repair agent for repairing DNAPL contamination based on chemical oxidation as claimed in claim 4, characterized in that: The repair agent is prepared and used immediately, the oxidizing core material of the coated oxidant is any one of potassium permanganate and sodium persulfate, and the coated oxidant is used within 48 hours after being compounded with the composite eluent.

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