A method for the remediation of an organically contaminated site using homogeneous catalysis of persulfate

Abstract

This invention discloses a homogeneous catalytic persulfate method for remediating organically contaminated sites. The method uses the water-soluble natural mineral carnallite as a catalyst and persulfate as an oxidant to remediate organic wastewater or organically contaminated soil within the site. This method eliminates the need for pre-adjustment of the site's pH value, and changes in the site's acidity or alkalinity have minimal impact on the removal efficiency of organic pollutants, thus avoiding secondary pollution. Furthermore, carnallite, as a homogeneous catalyst for remediating organically contaminated soil, offers advantages such as low remediation cost, strong diffusion capacity, and high catalytic efficiency.

Description

Technical fields:

[0001] This invention belongs to the field of organic contaminated site remediation technology, specifically relating to a method for homogeneous catalytic persulfate remediation of organic contaminated sites. Background technology:

[0002] Organic wastewater and contaminated soil within sites have been a focus of attention both domestically and internationally due to their harmful effects on the ecological environment and human health. Chemical oxidation is a commonly used technology for the remediation of organically contaminated sites. Among them, persulfate (PS) chemical oxidation technology has advantages such as high oxidation efficiency, mild reaction conditions, and easy transportation and storage of reagents, and is widely used for the oxidative remediation of organic wastewater or organically contaminated soil within sites.

[0003] PS, under the action of a catalyst, can generate sulfate free radicals with strong oxidizing activity to oxidize and degrade organic pollutants. Currently, the development of highly efficient activated PS catalysts is a research hotspot in the field of PS oxidation technology. PS catalysts are divided into homogeneous catalysts and heterogeneous catalysts. Among them, homogeneous catalysts can be completely dissolved in the aqueous phase. In the process of remediating organic wastewater / contaminated soil, homogeneous catalytic agents have the advantages of high mass transfer efficiency and fast reaction rate. 2+ and OH - It is a commonly used homogeneous PS catalyst; however, directly using Fe... 2+ The optimal pH range for homogeneous catalysis of PS is 3–4; therefore, the site pH needs to be adjusted to acidity before treatment. OH⁻ is used. - Homogeneous catalysts can catalyze PS, which can make the site alkaline and have a negative impact on the environment.

[0004] In summary, the search for a homogeneous catalyst that can efficiently catalyze the oxidation of organic pollutants in PS sites without pH adjustment is urgently needed in practical engineering applications for the remediation of organically contaminated sites using PS. However, relevant research is still scarce. This application utilizes a water-soluble natural mineral, carnallite (KCl·MgCl2·6H2O), as a homogeneous catalyst, which can efficiently catalyze the oxidation of organic pollutants in PS sites without pH adjustment, and the physicochemical properties of the site remain largely unchanged after the reaction. Summary of the Invention:

[0005] The purpose of this invention is to provide a method for homogeneous catalytic persulfate remediation of organically contaminated sites.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for homogeneous catalytic persulfate remediation of organically contaminated sites. The method is used to remediate organic wastewater or organically contaminated soil in the site. Carnallite and persulfate are added to the organic wastewater or organically contaminated soil in the site, and mechanical stirring is used to fully dissolve them, thereby oxidatively degrading the organic matter in the organic wastewater or organically contaminated soil in the site.

[0008] The specific process for remediating organic wastewater is as follows: obtain organic wastewater from the site, add carnallite and PS to the organic wastewater, mechanically stir to fully dissolve it, and react for 24-48 hours; the concentration of organic pollutants in the organic wastewater is 50-500 mg / L, the concentration of carnallite added to the organic wastewater is 0.2-2 g / L, and the concentration of PS added to the organic wastewater is 0.5-5 g / L.

[0009] The mass ratio of carnallite to PS is 1:1.5 to 1:2.5.

[0010] The pH value of the organic wastewater is 3 to 11, preferably 7 to 8.

[0011] The specific process for remediating organically contaminated soil is as follows: Obtain organically contaminated soil from the site, and prepare carnallite solution and PS solution by mixing 5% to 15% of the mass of the organically contaminated soil with water, respectively. Add the carnallite solution to the organically contaminated soil and mechanically stir for 0.5 to 3 hours, then add the PS solution and mechanically stir for another 0.5 to 3 hours. The moisture content of the organically contaminated soil is controlled to be 30% to 50% when adding the carnallite solution and PS solution.

[0012] After stirring evenly, let it stand for 24–48 hours.

[0013] The pH value of the organically contaminated soil is 3 to 11, preferably 7 to 8.

[0014] The site is a site contaminated with phenols, chlorinated hydrocarbons, or benzene compounds, etc., wherein the phenols are at least one of phenol, chlorophenol, etc., the benzene compounds are at least one of toluene or xylene, etc., and the chlorinated hydrocarbons are at least one of 1,2-dichloroethane, trichloroethylene, etc.

[0015] By using the above methods, the removal efficiency of organic pollutants in organic wastewater or organically contaminated soil in the site reaches more than 75% within 24 to 48 hours, preferably more than 90% within 48 hours.

[0016] Preferably, if the object being treated is organically contaminated soil, the amount of carnallite added is 10% to 12% of the mass of the organically contaminated soil, and the amount of PS added is 0.08% to 0.12% of the mass of the organically contaminated soil. The addition of the two solutions controls the moisture content of the organically contaminated soil to be 40% to 50%.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) Carnallite-catalyzed PS remediation of organic contaminated sites does not require prior pH adjustment, and changes in acidity and alkalinity have little impact on the removal efficiency of organic pollutants, and will not cause secondary pollution.

[0019] (2) Carnallite is an inexpensive natural mixed salt mineral. It has a low cost for catalyzing PS to remediate organically contaminated sites and has a significant advantage in practical applications.

[0020] (3) When remediating organically contaminated soil in ex-situ, the low soil moisture content makes it difficult for heterogeneous catalysts to diffuse effectively in the soil, resulting in waste of reagents and low pollutant removal efficiency. Compared with heterogeneous catalysts, carnallite, as a homogeneous catalyst, is completely soluble in water and has strong migration and diffusion capabilities in the soil, which can efficiently catalyze the remediation of organically contaminated soil with PS. Detailed implementation method:

[0021] To better understand the content of this invention, the following detailed description is provided in conjunction with the embodiments, but the embodiments of the invention are not limited thereto.

[0022] This invention uses carnallite as a homogeneous catalyst and persulfate as an oxidant for the remediation of organic wastewater or organically contaminated soil. It significantly improves the removal efficiency of organic pollutants without requiring pH adjustment and thus avoids secondary pollution. Experiments show that, under the same conditions, carnallite-catalyzed PS exhibits significantly better performance in removing organic pollutants than PS alone, and is also significantly superior to Fe under the same conditions. 2+ and OH - The effect of catalyzing PS.

[0023] The on-site working method for remediating organic wastewater is as follows: the organic wastewater is pumped into the reaction tank using a water pump, and homogeneous catalysts carnallite and persulfate are added to the organic wastewater. The mixture is then mechanically stirred to ensure complete dissolution, and ex-situ homogeneous catalytic oxidation is carried out to degrade the organic pollutants in the organic wastewater.

[0024] The on-site working method for remediating organically contaminated soil in the site is as follows: the organically contaminated soil is transferred from the excavation site to the reaction tank, the homogeneous catalyst carnallite and the oxidant persulfate are dissolved in water respectively, and then added to the organically contaminated soil. The mixture is mechanically stirred evenly, and ex-situ homogeneous catalytic oxidation is carried out to degrade the organic pollutants in the organically contaminated soil.

[0025] Example 1

[0026] The specific steps for the ex-situ homogeneous catalytic oxidation of 1,2-dichloroethane in organic wastewater are as follows:

[0027] In Example 1 of this invention, the concentration of 1,2-dichloroethane in the wastewater was 200 mg / L.

[0028] The organic wastewater was transferred to a reaction tank, and then carnallite catalyst and sodium persulfate oxidant were added. The concentration of carnallite in the organic wastewater was 0.5 g / L, and the concentration of sodium persulfate in the organic wastewater was 1 g / L. After mechanical stirring to ensure complete dissolution, the reaction was carried out for 24 hours. Organic pollutant water samples were taken after the reaction, and the residual organic pollutant content in the organic wastewater was calculated after testing and analysis.

[0029] The results showed that the concentration of 1,2-dichloroethane in the organic wastewater after the reaction was 5.8 mg / L, and the removal efficiency of 1,2-dichloroethane in the organic wastewater by carnallite-catalyzed sodium persulfate was 97.1%.

[0030] Example 2

[0031] The initial pH values ​​of the 1,2-dichloroethane wastewater in Example 1 were adjusted to 3.0 and 11.0, respectively, and then the 1,2-dichloroethane in the wastewater was degraded using carnallite-catalyzed sodium persulfate under the conditions of Example 1. In other words, only the pH of the 1,2-dichloroethane wastewater was changed to 3.0 and 11.0; the remaining steps were the same as in Example 1.

[0032] The results showed that the concentration of 1,2-dichloroethane in organic wastewater with an initial pH of 3.0 after the reaction was 9.6 mg / L, and the concentration was 10.6 mg / L in organic wastewater with an initial pH of 11.0. The removal efficiencies of carnallite-catalyzed sodium persulfate for 1,2-dichloroethane removal from organic wastewater were 95.2% and 94.7%, respectively. This indicates that the catalyst selected in this invention is applicable to organic wastewater with different acidity and alkalinity, and that the pH of the water body does not need to be adjusted in advance for organic wastewater remediation.

[0033] To more intuitively illustrate the data changes in Examples 1-2, as shown in Table 1:

[0034] Table 1 Comparison of the effects of carnallite-catalyzed sodium persulfate remediation of organic wastewater in the site under different conditions.

[0035]

[0036] The initial concentration of 1,2-dichloroethane in the organic wastewater was 200 mg / L, and the pH value of the organic wastewater did not change significantly before and after the reaction.

[0037] Example 3

[0038] The heterogeneous homogeneous catalytic oxidation of 2,4-dichlorophenol in organically contaminated soil, referred to as 2,4-dichlorophenol-contaminated soil, with a concentration of 250 mg / kg, was performed. The specific steps are as follows:

[0039] 1) Solution preparation: Dissolve 10% of the carnallite powder (by weight of organic polluted soil) and 0.1% of the sodium persulfate (by weight of organic polluted soil) in a certain amount of deionized water to obtain carnallite solution and sodium persulfate solution for later use;

[0040] The specified amount of deionized water refers to water that can completely dissolve carnallite and sodium persulfate while controlling the moisture content of the organically polluted soil to 50%.

[0041] 2) Adding a catalyst: Add the carnallite solution to the organically contaminated soil contaminated with 2,4-dichlorophenol and mechanically stir for 1 hour to ensure thorough mixing;

[0042] 3) Add oxidizing agent: Add sodium persulfate solution and mechanically stir for 1 hour to ensure thorough mixing;

[0043] 4) Static reaction: The organically contaminated soil mixed in step 3) was allowed to stand for 48 hours. 2,4-Dichlorophenol was extracted from the reacted organically contaminated soil sample, and the concentration of residual 2,4-dichlorophenol in the organically contaminated soil was calculated through analysis.

[0044] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 11.0 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by carnallite-catalyzed sodium persulfate was 95.6%.

[0045] Example 4

[0046] In this embodiment, the process of oxidizing 2,4-dichlorophenol in organically contaminated soil by sodium persulfate catalyzed by carnallite is the same as in Example 3, except that the concentration of 2,4-dichlorophenol is 250 mg / kg. The difference is that the amount of sodium persulfate added is equivalent to 0.05% of the mass of the organically contaminated soil, and the remaining steps are the same as in Example 3.

[0047] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 59.8 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by sodium persulfate catalyzed by carnallite was 76.1%.

[0048] Example 5

[0049] In this embodiment, the process of oxidizing 2,4-dichlorophenol in organically contaminated soil by sodium persulfate catalysis with carnallite is the same as in Example 3, except that the concentration of 2,4-dichlorophenol is 250 mg / kg. The difference is that the soil moisture content is controlled at 30%, and the remaining steps are the same as in Example 3.

[0050] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 48.8 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by sodium persulfate catalyzed by carnallite was 80.5%.

[0051] Example 6

[0052] The initial pH values ​​of the organically contaminated soil with 2,4-dichlorophenol in Example 3 were adjusted to 3.0 and 11.0, respectively. Then, the 2,4-dichlorophenol was degraded by sodium persulfate catalyzed with carnallite under the conditions of Example 3. That is, only the pH of the organically contaminated soil with 2,4-dichlorophenol was changed to 3.0 and 11.0, and the remaining steps were the same as in Example 3.

[0053] The results showed that the concentration of 2,4-dichlorophenol in organically contaminated soil with an initial pH of 3.0 after the reaction was 13.0 mg / kg, and the concentration in organically contaminated soil with an initial pH of 11.0 was 12.0 mg / kg. The removal efficiencies of carnallite-catalyzed sodium persulfate for 2,4-dichlorophenol in organically contaminated soil were 94.8% and 95.2%, respectively. This indicates that the catalyst selected in this invention is applicable to organically contaminated soils with different acidity and alkalinity, and it is not necessary to adjust the soil pH in advance for the remediation of organically contaminated soil.

[0054] Example 7

[0055] The ex-situ homogeneous catalytic oxidation of toluene in organically contaminated soil, known as toluene-contaminated soil, with a toluene concentration of 300 mg / kg, was performed. The specific steps are as follows:

[0056] 1) Solution preparation: Dissolve 10% of the carnallite powder (by weight of organic polluted soil) and 0.1% of the sodium persulfate (by weight of organic polluted soil) in a certain amount of deionized water to obtain carnallite solution and sodium persulfate solution for later use;

[0057] The specified amount of deionized water refers to water that can completely dissolve carnallite and sodium persulfate while controlling the moisture content of the organically polluted soil to 50%.

[0058] 2) Adding a catalyst: Add the carnallite solution to the toluene-contaminated soil and mechanically stir for 1 hour to ensure thorough mixing;

[0059] 3) Add oxidant: Add sodium persulfate solution to the toluene-contaminated soil treated in step 2) and mechanically stir for 1 hour to ensure thorough mixing;

[0060] 4) Static reaction: The organically contaminated soil mixed in step 3) is allowed to stand for 48 hours to react. A sample of the reacted organically contaminated soil is taken, and toluene is extracted and analyzed to calculate the concentration of residual toluene in the soil.

[0061] The results showed that the toluene concentration in the organically polluted soil after the reaction was 19.8 mg / kg, and the removal efficiency of toluene in the organically polluted soil by carnallite-catalyzed sodium persulfate was 93.4%.

[0062] To more intuitively display the data changes in Examples 3-7, as shown in Table 2:

[0063] Table 2 Comparison of the effects of carnallite-catalyzed sodium persulfate remediation of organic-contaminated soil in the site under different conditions.

[0064]

[0065] The initial concentration of 2,4-dichlorophenol in the organically contaminated soil was 250 mg / kg; the initial concentration of toluene was 300 mg / kg. The pH value of the organically contaminated soil did not change significantly before and after the reaction.

[0066] Comparative Example 1

[0067] In Example 3, the carnallite-catalyzed sodium persulfate was replaced with FeSO4-catalyzed sodium persulfate, and the soil was treated for 2,4-dichlorophenol contamination under the conditions described in Example 3. Specifically, FeSO4, equivalent to 10% of the mass of the organically contaminated soil, was prepared as a solution and added to the 2,4-dichlorophenol contaminated soil. The remaining steps were the same as in Example 3.

[0068] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 113.0 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by FeSO4-catalyzed sodium persulfate was 54.8%.

[0069] Comparative Example 2

[0070] In Example 3, the carnallite-catalyzed sodium persulfate was replaced with NaOH-catalyzed sodium persulfate, and the soil was treated for 2,4-dichlorophenol contamination under the conditions described in Example 3. Specifically, a solution of NaOH equivalent to 10% of the mass of the organically contaminated soil was prepared and added to the 2,4-dichlorophenol contaminated soil. The remaining steps were the same as in Example 3.

[0071] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 87.3 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by sodium persulfate catalyzed by NaOH was 65.1%.

[0072] Comparative Example 3

[0073] In Example 3, the carnallite-catalyzed sodium persulfate was replaced with KCl-catalyzed sodium persulfate, and the soil was treated for 2,4-dichlorophenol contamination under the conditions described in Example 3. Specifically, a solution of KCl equivalent to 10% of the mass of the organically contaminated soil was prepared and added to the 2,4-dichlorophenol contaminated soil. The remaining steps were the same as in Example 3.

[0074] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 99.5 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by KCl-catalyzed sodium persulfate was 60.2%.

[0075] Comparative Example 4

[0076] In Example 3, the carnallite-catalyzed sodium persulfate was replaced with MgCl2-catalyzed sodium persulfate, and the soil was treated according to the conditions in Example 3. Specifically, MgCl2, equivalent to 10% of the mass of the organically contaminated soil, was prepared into a solution and added to the 2,4-dichlorophenol-contaminated soil. The remaining steps were the same as in Example 3.

[0077] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 126.0 mg / kg, and the removal efficiency of 2,4-dichlorophenol in the organically polluted soil by sodium persulfate catalyzed by MgCl2 was 49.6%.

[0078] Comparative Example 5

[0079] In Example 3, the sodium persulfate catalyzed by carnallite was replaced with sodium persulfate alone. The soil was then treated for 2,4-dichlorophenol contamination under the conditions described in Example 3. Specifically, a solution of sodium persulfate equivalent to 0.1% of the organic contaminated soil mass was added to the 2,4-dichlorophenol contaminated soil. The remaining steps were the same as in Example 3.

[0080] The results showed that the concentration of 2,4-dichlorophenol in the organically polluted soil after the reaction was 182.5 mg / kg, and the removal efficiency of sodium persulfate for 2,4-dichlorophenol in the organically polluted soil was 27.0%.

[0081] Comparative Example 6

[0082] In Example 3, the sodium persulfate catalyzed by carnallite was replaced with sodium persulfate catalyzed by carnallite-supported biochar material, and the mixture was used for the remediation of 2,4-dichlorophenol-contaminated soil under the conditions described in Example 3. Specifically, a slurry of biochar material equivalent to 10% of the mass of the organically contaminated soil was prepared and added to the 2,4-dichlorophenol-contaminated soil, with the remaining steps identical to those in Example 3.

[0083] The results showed that the concentration of 2,4-dichlorophenol in organically polluted soil with an initial pH of 3.0 after the reaction was 68.8 mg / kg, and the concentration of 2,4-dichlorophenol in organically polluted soil with an initial pH of 11.0 was 79.0 mg / kg. The removal efficiencies of sodium persulfate catalyzed by biochar material supported on carnallite for 2,4-dichlorophenol in organically polluted soil were 72.5% and 68.4%, respectively.

[0084] To more intuitively display the data changes in comparative examples 1-6, see Table 3:

[0085] Table 3 Comparison of the effects of different catalysts on the remediation of organic-contaminated soil with sodium persulfate in the site.

[0086]

[0087] The amount of catalyst added was equivalent to 10% of the mass of organically contaminated soil, the amount of sodium persulfate added was equivalent to 0.1% of the mass of organically contaminated soil, and the initial concentration of 2,4-dichlorophenol contaminated soil was 250 mg / kg.

[0088] In Table 3 above, under the same reaction conditions of pH 7.5, the removal efficiencies of various homogeneous catalysts were significantly weaker than those of the carnallite catalyst of this application, with removal efficiencies below 65%. Furthermore, in Comparative Example 6, which used carnallite as a raw material and calcined it with biochar to form a heterogeneous catalyst, the removal efficiencies were all lower than those in Example 6 of this application under different pH conditions, all below 75%. The removal efficiency fluctuated significantly with changes in pH. When using heterogeneous catalysts for ex-situ soil remediation, the heterogeneous catalysts are not easily dispersed uniformly in the soil, and the biochar catalyst using carnallite as a raw material has a long catalytic time, which easily leads to the risk of prolonged oxidant failure.

[0089] This invention directly uses natural carnallite as a homogeneous catalyst to catalyze the remediation of organically contaminated sites using polystyrene (PS). Experimental results show that carnallite can effectively remove organic pollutants from the site, and no pH adjustment is required before use, thus avoiding secondary pollution. Under the same conditions, the removal rate of organic pollutants by PS catalyzed by carnallite is significantly higher than that by Fe. 2+ Catalysts for PS and OH -Furthermore, carnallite-catalyzed PS exhibits excellent removal effects on organic pollutants in both acidic and alkaline sites without altering the site pH, demonstrating advantages such as high catalytic performance, low remediation costs, and environmental friendliness.

[0090] The method of this invention is applicable to both ex-situ remediation sites and in-situ remediation, with a wider range of applications, higher removal efficiency, lower time cost, and the ability to achieve rapid remediation while saving on reagent usage.

[0091] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for homogeneous catalytic persulfate remediation of organically contaminated sites, characterized in that, The method is used to remediate organic wastewater or organically contaminated soil in the site. Carnallite and persulfate are added to the organic wastewater or contaminated soil in the site, and mechanically stirred to fully dissolve them, thereby oxidizing and degrading the organic matter in the organic wastewater or organically contaminated soil in the site. The pH value of the site is 3~11. Without changing the pH of the site, carnallite-catalyzed PS has a good removal effect on organic pollutants in both acidic and alkaline sites, and is suitable for both ex-situ remediation and in-situ remediation. Organic wastewater from the site was collected, and carnallite and persulfate were added. The mixture was mechanically stirred until fully dissolved and reacted for 24–48 h. The concentration of organic pollutants in the organic wastewater was 50–500 mg / L, the concentration of carnallite in the organic wastewater was 0.2–2 g / L, and the concentration of persulfate in the organic wastewater was 0.5–5 g / L. The mass ratio of carnallite to persulfate was 1:1.5–1:2.

5. Alternatively, obtain organically contaminated soil from the site, and prepare carnallite solution and persulfate solution by mixing 5% to 15% of the mass of the organically contaminated soil with water, and add carnallite solution and persulfate solution respectively. Add carnallite solution to organically contaminated soil and stir mechanically for 0.5 to 3 hours, then add persulfate solution and stir mechanically for 0.5 to 3 hours. The moisture content of organically contaminated soil should be controlled at 30% to 50% when adding carnallite solution and persulfate solution. After stirring evenly, let stand for 24 to 48 hours.

2. The method for homogeneous catalytic persulfate remediation of organically contaminated sites according to claim 1, characterized in that, The amount of carnallite added is equivalent to 10% to 12% of the mass of the organic polluted soil, and the amount of persulfate added is equivalent to 0.08% to 0.12% of the mass of the organic polluted soil. The addition of the two solutions controls the moisture content of the organic polluted soil to be 40% to 50%.

3. The method for homogeneous catalytic persulfate remediation of organically contaminated sites according to claim 1 or 2, characterized in that, The site is a site contaminated with phenols, chlorinated hydrocarbons, or benzene compounds, wherein the phenols are at least one of phenol and chlorophenol, the benzene compounds are at least one of toluene or xylene, and the chlorinated hydrocarbons are at least one of 1,2-dichloroethane and trichloroethylene.

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