Method for removing new pollutants in underground water by injection type in-situ reaction zone

Abstract

The invention discloses a method for removing new pollutants in underground water through an injection type in-situ reaction zone, and belongs to the field of underground water pollution remediation of polluted sites. The method comprises the following steps: (1) preparing solid particle catalyst slurry; (2) preparing an oxidant solution; and (3) respectively and synchronously injecting the catalyst slurry obtained in the step (1) and the oxidant solution obtained in the step (2) into a water-containing layer, wherein the catalyst slurry and the oxidant solution react in a water environment to form an in-situ reaction zone. The catalyst slurry is prepared by using the non-soluble iron-manganese catalyst, so that the iron-manganese catalyst is prevented from being dissolved in water too early to generate ferrous ions, and the self-annihilation reaction and the loss of an oxidizing agent caused by instantaneous mass generation of free radicals due to too early activation of persulfate are avoided, so that the utilization rate of the oxidizing agent is effectively improved, and the medicament cost is saved.

Description

Technical Field

[0001] The invention belongs to the field of groundwater pollution remediation in contaminated sites and relates to a method for removing new pollutants in groundwater with an injection-type in-situ reaction zone. Background Art

[0002] New pollutants refer to a class of chemical substances that can be detected in the environment and natural ecosystems and can pose greater risks and hidden dangers to human health and environmental safety even if they enter at low doses. New pollutants that are widely concerned at home and abroad mainly include persistent organic pollutants, endocrine disruptors, antibiotics, microplastics, etc. that are controlled by international conventions. They generally have the characteristics of more serious hazards, more hidden risks, environmental persistence, wide sources, and vertical complexity. New pollutants have the characteristics of biological toxicity, environmental persistence, and bioaccumulation, but they have not yet been included in management or the existing management measures are insufficient. They are relatively new compared to traditional pollutants that have been regulated. New pollutants enter groundwater and pollute water resources. Their low-dose high toxicity characteristics pose potential hazards to the ecological environment and human health. Therefore, it is of great significance to remove new pollutants in groundwater and reduce or eliminate the hazards caused by water pollution.

[0003] In-situ chemical oxidation (ISCO) technology is a method for treating soil and groundwater pollution in situ at contaminated sites. It uses chemical oxidation reactions to degrade organic pollutants and produce harmless substances by injecting oxidants such as permanganate, persulfate, hydrogen peroxide and ozone into the contaminated area. This method can avoid the pumping and treatment process required for ex-situ remediation, as well as the process of excavating soil and installing remediation reaction walls, thereby effectively reducing remediation costs and environmental disturbances. It has been considered a new groundwater contaminant remediation technology with great application potential.

[0004] Persulfate is an oxidant commonly used in ISCO technology. However, its low oxidation potential and chemical stability result in limited oxidation capacity for some refractory organic matter. Therefore, it is necessary to use specific activation technology to generate free radical species with stronger oxidation capacity. Iron-manganese catalyst is a catalyst used to promote chemical reactions. It is composed of two metals, iron and manganese. It has high catalytic activity and stability and can be used for a variety of reaction types. For example, it can be used to catalyze oxidation reactions. Therefore, iron-manganese catalyst is a more ideal catalyst in in-situ chemical oxidation technology. However, since the divalent iron ions formed by the iron-manganese catalyst after dissolving in water react very quickly with persulfate, when it is injected into the aquifer in the form of a solution through an injection well, it will quickly react with persulfate at the outlet to generate a large number of free radicals. However, these free radicals are often annihilated before they diffuse into the pollution plume, resulting in the loss of persulfate. At this time, the demand for oxidants will increase significantly, the cost of remediation will increase, and the remediation cycle will be extended.

[0005] Therefore, it is necessary to provide a method for removing new pollutants in groundwater by an injection-type in-situ reaction zone, which can effectively improve the degradation performance of persulfate on new pollutants while avoiding the annihilation of free radical species and loss of oxidant caused by excessive activation of oxidant, thereby improving the efficiency of pollution remediation and saving reagent costs. Summary of the invention

[0006] In order to overcome the problems in the background technology, the present invention prepares the catalyst slurry by using an insoluble iron-manganese catalyst, avoids the iron-manganese catalyst from being dissolved in water too early to produce divalent iron ions, avoids the premature activation of persulfate, causes the instantaneous generation of free radicals in large quantities, and causes self-annihilation reaction, causing the loss of oxidant, so that persulfate and catalyst slurry can be in the process of migration with groundwater flow, and gradually catalytic activation reaction occurs, slowly releases free radicals (such as hydroxyl radicals, sulfate radicals, etc.), forms an in-situ reaction zone, and oxidative degradation is performed on the pollutants flowing synchronously through the in-situ reaction zone. Thereby improving the use efficiency of persulfate, giving full play to the oxidant degradation effect, and helping to save the cost of medicine.

[0007] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The method comprises the following steps:

[0009] (1) preparing a solid particle catalyst slurry: adding an insoluble iron-manganese catalyst to water, and subjecting the mixture to ultrasonic treatment at room temperature to obtain an iron-manganese catalyst slurry; dissolving xanthan gum powder in water, stirring the mixture to form a uniform milky white slurry, and adding the milky white slurry to the iron-manganese catalyst slurry, subjecting the mixture to ultrasonic treatment to obtain a catalyst slurry;

[0010] (2) preparing an oxidant solution: dissolving persulfate powder in water to obtain an oxidant solution;

[0011] (3) The catalyst slurry obtained in step (1) and the oxidant solution obtained in step (2) are respectively and simultaneously injected into the aquifer, and the catalyst slurry and the oxidant solution react in the water environment to form an in-situ reaction zone.

[0012] Preferably, the insoluble iron-manganese catalyst comprises an iron-manganese oxide catalyst.

[0013] Preferably, in step (1), the solid-to-liquid ratio of the insoluble iron-manganese catalyst to water is 1.3 g:1 L.

[0014] Preferably, in step (1), the solid-liquid ratio of xanthan gum powder to water is 1 mg:1 ml.

[0015] Preferably, in the step (1), the volume ratio of the milky white slurry added to the iron-manganese catalyst slurry is: milky white slurry: iron-manganese catalyst slurry = 3:10.

[0016] Preferably, in step (1), xanthan gum powder is dissolved in 60°C water and stirred while maintaining the temperature at 60°C.

[0017] Preferably, in step (1), the ultrasonic treatment time for both times is 20 min, the ultrasonic treatment power is 200 W, and the ultrasonic frequency is 40 KHz.

[0018] Preferably, in step (2), the concentration of the oxidant solution is 100-200 times the concentration of the target pollutant.

[0019] Preferably, in step (3), the ratio of the catalyst slurry injection rate to the oxidant solution injection rate is 17:1.

[0020] Preferably, the specific preparation method of the insoluble iron-manganese catalyst is as follows: first, ferrous sulfate heptahydrate and potassium permanganate are dissolved in water to obtain an iron-manganese mixed solution, wherein the molar ratio of iron in ferrous sulfate heptahydrate to manganese in potassium permanganate is Fe:Mn=3:1, and then a NaOH solution with a concentration of 2 mol / L is added to the iron-manganese mixed solution until the pH value of the liquid reaches 7.0-8.0, and the addition of the NaOH solution is stopped, and then the liquid is stirred at a speed of 200 rpm for 60 minutes, and then allowed to stand for 12 hours, the liquid is filtered and washed, and the filtered solid matter is dried at 40°C for 24 hours, and the dried solid matter is ground into powder to obtain an insoluble iron-manganese catalyst. Since it is necessary to detect the change in the pH value of the liquid during the addition of the NaOH solution, the rate of adding the NaOH solution needs to be slow. At the same time, the amount of water is sufficient to ensure that the added ferrous sulfate heptahydrate and potassium permanganate are completely dissolved, and the water can be excessive.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention uses an insoluble iron-manganese catalyst to prepare a catalyst slurry, thereby preventing the iron-manganese catalyst from dissolving in water too early to produce divalent iron ions, and preventing the premature activation of persulfate from causing instantaneous large-scale generation of free radicals and causing self-annihilation reactions, thereby effectively improving the utilization rate of the oxidant, helping to improve the degradation rate of the target pollutant, and saving the cost of the agent.

[0023] 2. Since the present invention uses an insoluble iron-manganese catalyst to prepare the catalyst slurry, during the injection process, the iron-manganese catalyst enters the aquifer in the form of solid particles, which has a certain impact on the fluidity of the slurry. The present invention prepares the catalyst slurry by adding xanthan gum, and uses the xanthan gum to lubricate the solid particles of the iron-manganese catalyst, thereby reducing the negative impact of the solid particles on the injection of the catalyst slurry, and facilitating the smooth injection of the catalyst slurry into the aquifer and its movement in the aquifer.

[0024] 3. The present invention activates persulfate by an iron-manganese catalyst to efficiently generate free radicals, thereby enhancing the oxidative degradation effect of persulfate on target pollutants.

[0025] 4. The present invention uses an insoluble iron-manganese catalyst to catalytically activate persulfate. The iron-manganese catalyst can maintain stability in the form of solid particles in groundwater seepage for a long period of time, and the amount of iron-manganese ion seepage is maintained at a low level, reducing or even avoiding the problem of secondary water pollution caused by the addition of the iron-manganese catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process of the method of the present invention;

[0027] Figure 2 This is a schematic diagram of a sand column simulation experiment of the present invention;

[0028] Figure 3 This is a real shot of the sand column simulation experiment of the present invention;

[0029] Figure 4 This is the electron spin resonance magnetic spectrum of the iron-manganese catalyst of the present invention activating persulfate to generate free radicals. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with specific embodiments.

[0031] In the examples and comparative examples of the present invention, chemical reagents not otherwise specified were all commercially available analytically pure reagents for the experiments.

[0032] In the examples and comparative examples of the present invention, the new pollutant is bisphenol A (BPA), which is an important chemical organic raw material. It has been proven to have endocrine disrupting effects, is a typical new pollutant, and has been frequently detected in groundwater environments. Its low-dose high toxicity characteristics pose potential hazards to the ecological environment and human health.

[0033] Example 1

[0034] This embodiment removes pollution from groundwater according to the following method:

[0035] (1) Weigh ferrous sulfate heptahydrate and potassium permanganate according to a molar ratio of Fe:Mn=3:1, and dissolve the weighed ferrous sulfate heptahydrate and potassium permanganate in water. The dissolution process is observed by observing the dissolution of ferrous sulfate heptahydrate and potassium permanganate until they are completely dissolved to obtain an iron-manganese mixed solution. Then, slowly add a 2 mol / L NaOH solution to the iron-manganese mixed solution until the pH value of the liquid reaches 7.0-8.0, stop adding the NaOH solution, and then stir the liquid at a speed of 200 rpm for 60 minutes, then let it stand for 12 hours, filter and wash the liquid, and dry the filtered solid matter at 40°C for 24 hours, grind the dried solid matter into powder, and obtain an insoluble iron-manganese catalyst.

[0036] (2) 1.95 g of the iron-manganese catalyst powder prepared in step (1) was added to 1.5 L of ultrapure water and ultrasonicated at room temperature for 20 min; 450 mg of xanthan gum was dissolved in 450 ml of ultrapure water at 60° C. and stirred at 800 r / min for 20 min to form a uniform milky white slurry; the dissolved xanthan gum solution was poured into the beaker containing the iron-manganese catalyst slurry and ultrasonicated for 20 min to form a catalyst slurry; a 35.0 mM potassium permonosulfate solution was prepared with ultrapure water. The catalyst slurry and potassium permonosulfate solution were injected into the simulated groundwater prepared in this embodiment at pump speeds of 0.8 ml / min and 0.047 ml / min, respectively, to form an in-situ reaction zone.

[0037] This example uses a sand column simulation method to conduct experiments (such as Figure 2 , 3 The sand column is composed of quartz sand with fixed particle size filled in an organic glass column. From bottom to top, it is divided into water distribution area, reaction area, and water outlet area. The inner diameter of the organic glass column is 5 cm, the total length is 50 cm, and the heights of the water distribution area, reaction area, and water outlet area are 3 cm, 44 cm, and 3 cm respectively. The main pollutant in the simulated groundwater is bisphenol A, with a bisphenol A content of 0.175 mM. At the same time, the simulated groundwater also contains 5 mM HCO 3 - , 2 mM Ca 2+ , 0.3 mM Mg 2 + , 0.2 mM Cl - During the experiment, simulated groundwater was injected from the lower end of the sand column through a peristaltic pump (with a set flow rate) (e.g. Figure 2 The simulated groundwater was then filtered out of the sand column, and the water was then filtered out. The water ..., and the water was then filtered out. The water was then filtered out, and the water was then filtered out. The water was then filtered out, and the water was then filtered out. The water was then filtered out, and the water was then filtered out. The water was then filtered out, and the water was then filtered out.

[0038] Example 2

[0039] This example uses the same method as Example 1 to carry out the simulation experiment, except that in this example, the concentration of the potassium permonosulfate solution is 17.5 mM.

[0040] In this embodiment, the removal effect of bisphenol A is about 70%.

[0041] Example 3

[0042] This example uses the same method as Example 1 to carry out the simulation experiment, except that in this example, the concentration of the potassium permonosulfate solution is 26.2 mM.

[0043] In this embodiment, the removal effect of bisphenol A is about 90%.

[0044] Example 4

[0045] This example uses the same method as Example 1 to carry out the new pollutant removal experiment, except that in this example, the catalyst slurry and oxidant solution are injected into the actual aquifer, and the background chemical components of the groundwater in the aquifer include: 2.982mM HCO 3 - , 2.525 mM Ca 2+ , 1.607 mM Mg 2+ , 1.004 mM Cl - .

[0046] In this embodiment, the removal rate of bisphenol A is 78%.

[0047] Comparative Example 1

[0048] This comparative example uses the same method as Example 1 to carry out simulation experiments, except that the catalyst in this example is ferrous sulfate solution.

[0049] In this comparative example, the removal rate of bisphenol A is about 43%.

[0050] Comparative Example 2

[0051] This comparative example uses the same method as Example 1 to carry out a simulation experiment, except that: xanthan gum is not added to the catalyst slurry of this comparative example.

[0052] By comparing Example 1 with Comparative Example 1, it can be seen that the removal rate of bisphenol A in Comparative Example 1 is significantly reduced. The reason is that after ferrous sulfate is dissolved in water, divalent iron ions are formed. Therefore, after the ferrous sulfate solution contacts the persulfate oxidant, it reacts very quickly to generate free radicals. Since the simulated groundwater is introduced from the bottom of the sand column at a slower flow rate, it first needs to pass through the water distribution area. During this period of time, the simulated groundwater does not enter the reaction zone, so the simulated groundwater does not contact the oxidant. Instead, after a certain period of time, the simulated groundwater enters the reaction zone and contacts the oxidant. However, after a certain period of time, the free radicals generated in Comparative Example 1 undergo a self-annihilation reaction, resulting in a large reduction in free radicals under the same amount of oxidant added, affecting the degradation effect of bisphenol A.

[0053] pass Figure 3 It can be seen (Example 1 and Comparative Example 2) that the iron-manganese catalyst prepared by the present invention is not dissolved in water. At the same time, it can be clearly seen from the figure that after the catalyst slurry without xanthan gum (Comparative Example 2) is passed into the sand column, the number of iron-manganese catalyst particles accumulated at the bottom of the sand column is relatively large, while after the catalyst slurry with xanthan gum is passed into the sand column, the number of iron-manganese catalyst particles accumulated at the bottom of the sand column is relatively small, indicating that the addition of xanthan gum is conducive to the movement of iron-manganese catalyst particles in the sand column, that is, it proves that after the catalyst slurry of the present invention is injected into the aquifer, its performance of moving with the flow of liquid is better, thereby reducing the negative impact of the solid particle catalyst slurry on fluidity.

[0054] pass Figure 4 It can be seen that the insoluble catalyst prepared by the present invention can effectively activate persulfate to generate free radicals.

[0055] In summary, the present invention uses an insoluble iron-manganese catalyst to prepare the catalyst slurry, thereby avoiding the catalyst from catalytically activating the oxidant too early and too quickly, resulting in the effective ingredients not playing a role and annihilation, effectively improving the utilization rate of the oxidant, helping to improve the pollutant removal rate, and saving the cost of the agent.

[0056] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for removing new pollutants from groundwater in an injection-type in-situ reaction zone, characterized in that: The method comprises the following steps: (1) preparing a solid particle catalyst slurry: adding an insoluble iron-manganese catalyst to water, and subjecting the mixture to ultrasonic treatment at room temperature to obtain an iron-manganese catalyst slurry; dissolving xanthan gum powder in water, stirring the mixture to form a uniform milky white slurry, and adding the milky white slurry to the iron-manganese catalyst slurry, subjecting the mixture to ultrasonic treatment to obtain a catalyst slurry; (2) preparing an oxidant solution: dissolving persulfate powder in water to obtain an oxidant solution; (3) The catalyst slurry obtained in step (1) and the oxidant solution obtained in step (2) are respectively and simultaneously injected into the aquifer, and the catalyst slurry and the oxidant solution react in the water environment to form an in-situ reaction zone.

2. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: The insoluble iron-manganese catalyst includes an iron-manganese oxide catalyst.

3. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (1), the solid-to-liquid ratio of the insoluble iron-manganese catalyst to water is 1.3 g:1 L.

4. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (1), the solid-liquid ratio of xanthan gum powder to water is 1 mg:1 ml.

5. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (1), the volume ratio of the milky white slurry added to the iron-manganese catalyst slurry is: milky white slurry: iron-manganese catalyst slurry = 3:

10.

6. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (1), xanthan gum powder is dissolved in 60° C. water and stirred while maintaining the temperature at 60° C.

7. A method for removing new pollutants from groundwater in an injection-type in-situ reaction zone according to any one of claims 1 to 6, characterized in that: In the step (1), the ultrasonic treatment time is 20 min for each of the two times, the ultrasonic treatment power is 200 W for each time, and the ultrasonic frequency is 40 KHz for each time.

8. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (2), the concentration of the oxidant solution is 100-200 times the concentration of the target pollutant.

9. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: In the step (3), the ratio of the catalyst slurry injection rate to the oxidant solution injection rate is 17:

1.

10. The method for removing new pollutants from groundwater by injection-type in-situ reaction zone according to claim 1, characterized in that: The specific preparation method of the insoluble iron-manganese catalyst is as follows: first, ferrous sulfate heptahydrate and potassium permanganate are dissolved in water to obtain an iron-manganese mixed solution, wherein the molar ratio of iron in ferrous sulfate heptahydrate to manganese in potassium permanganate is Fe:Mn=3:1, and then a NaOH solution with a concentration of 2 mol / L is added to the iron-manganese mixed solution until the pH value of the liquid reaches 7.0-8.0, and the addition of the NaOH solution is stopped, and then the liquid is stirred at a speed of 200 rpm for 60 minutes, and then allowed to stand for 12 hours, the liquid is filtered and washed, and the filtered solid matter is dried at 40°C for 24 hours, and the dried solid matter is ground into powder to obtain the insoluble iron-manganese catalyst.

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