Compositions for groundwater remediation and methods of use and application thereof

Abstract

The present application relates to the field of groundwater remediation, and discloses a composition for groundwater remediation, application and method thereof.The composition contains a slow-release oxidant and an iron-based molecular sieve composite material; the slow-release oxidant has a core-shell structure, the shell layer is polylactic acid, and the core layer is a metal peroxide and citric acid; the iron-based molecular sieve composite material contains Silicalite-1 molecular sieve and Fe element loaded on the Silicalite-1 molecular sieve, and the weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is greater than or equal to 45.The composition for groundwater remediation has the advantages of high activity and durability, can achieve efficient and long-acting degradation of methyl tert-butyl ether in groundwater, and can more effectively remediate groundwater.

Description

Technical Field

[0001] This invention relates to the field of groundwater remediation, and more specifically to a composition for groundwater remediation and its application and method. Background Technology

[0002] Methyl tert-butyl ether (MTBE) is an oxygen-containing compound that increases the oxygen content in gasoline, reduces the emission of incomplete combustion oxides in exhaust gases, improves the octane rating of gasoline, and enhances its anti-knock properties. It also boasts advantages such as low price, high octane rating, and good compatibility with gasoline, making it widely used as a gasoline additive. Currently, MTBE has become the second most common pollutant detected in urban groundwater. Faced with the widespread nature of MTBE pollution and the urgency of its remediation, researchers have employed various remediation technologies for MTBE-contaminated groundwater, primarily including air stripping, adsorption, chemical oxidation, electrochemical oxidation, and bioremediation. Air stripping is an ex-situ treatment technology that utilizes compressed air to contact the contaminated water, allowing dissolved volatile organic compounds (VOCs) to diffuse through the gas-liquid interface into the gas phase, thereby removing the pollutants. However, due to the low Henry's constant of MTBE (H / RT = 0.0216), stripping low concentrations of MTBE from water requires a high gas-to-water ratio and a long residence time. Therefore, research on using air stripping alone to remove MTBE is relatively limited. Chemical oxidation refers to the use of oxidants to generate free radicals with high redox potentials, which then react chemically with organic pollutants, decomposing them into less toxic or non-toxic compounds. Currently, oxidants used in MTBE oxidation research include potassium permanganate, Fenton's reagent, persulfate, hydrogen peroxide, and ozone. Different oxidants exhibit significant differences in their oxidizing power for MTBE. Among them, the hydroxyl radical (·OH) has the highest redox potential (E = 2.8 V) and a reaction rate constant with MTBE of 1.6 × 10⁹ M⁻¹. –1 .S –1However, most processes achieve optimal performance under acidic conditions, and the toxicity and mineralization degree of MTBE degradation intermediates need further evaluation. Electrochemical oxidation refers to using the treatment system as an electrolytic cell, directly oxidizing and degrading pollutants at the anode through an applied electric field, or indirectly participating in the oxidation reaction by generating strong oxidizing substances during electrolysis. Existing technologies use metallic nickel as the anode to study the performance of MTBE degradation in different electrolyte environments. The results show that the effectiveness of electrochemical oxidation depends on the alkaline environment; the NiOOH / Ni(OH)2 layer deposited on the anode surface acts as an intermediary for anode electron transfer, and pH control is a challenge for in-situ remediation of groundwater using electrochemical oxidation technology. Bioremediation utilizes functional microorganisms to degrade organic pollutants in the environment. The ether bond in the MTBE molecule has a high dissociation energy (360 kJ / mol), and the large steric hindrance of the tert-butyl group also increases the molecular stability. During the biodegradation of MTBE, the accumulation of the intermediate product tert-butanol increases its toxicity to organisms. Therefore, MTBE is not easily biodegraded in either aerobic or anaerobic environments, and the biodegradation rate of MTBE under anaerobic conditions is 500-1500 times lower than under aerobic conditions. Although some studies have shown that some strains can degrade MTBE, it is difficult to isolate strains from enrichment cultures when MTBE is used as the sole carbon source, and only a few strains are successfully cultured, further limiting the application of this method. Permeable reactive barriers (PRBs) are techniques that place a barrier medium perpendicular to the direction of groundwater flow. When pollutants flow through the barrier under the influence of a natural hydraulic gradient, they react with a certain thickness of the reactive medium, fixing or converting the pollutants into less toxic or non-toxic forms. The advantage is that the reactive medium can provide long-term remediation with minimal disturbance to the ecological environment. Currently, permeable reactive barriers are one of the most widely researched and applied technologies for treating polluted groundwater.

[0003] Existing literature on the use of PRB to degrade MTBE all employs bioreactor media, utilizing microorganisms to degrade pollutants. Generally, the reaction medium needs to provide functional microorganisms with the necessary nutrients and electron acceptors. However, due to the limited oxygen and nutrients in groundwater, coupled with the oxygen consumption during dissolved organic matter degradation, which easily leads to foul-smelling water bodies, the microbial growth environment becomes harsh, inhibiting pollutant degradation to some extent and resulting in poor long-term degradation stability. Therefore, it is necessary to research and develop a groundwater remediation composition applicable to permeable walls as a barrier medium to improve the degradation efficiency and long-term stability of methyl tert-butyl ether in groundwater. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of difficult degradation of organic pollutants in groundwater, especially the high difficulty in degrading methyl tert-butyl ether in groundwater, resulting in low degradation efficiency and poor long-term stability. This invention provides a composition for groundwater remediation, its application, and a method thereof. This composition for groundwater remediation has advantages such as high activity and durability, and can achieve efficient and long-term degradation of methyl tert-butyl ether in groundwater, thus more effectively remediating groundwater.

[0005] To achieve the above objectives, the present invention provides a composition for groundwater remediation, the composition comprising a slow-release oxidant and an iron-based molecular sieve composite material;

[0006] The slow-release oxidant has a core-shell structure, with the shell being polylactic acid and the core being a metal peroxide and citric acid;

[0007] The iron-based molecular sieve composite material contains Silicalite-1 molecular sieve and Fe element supported on Silicalite-1 molecular sieve;

[0008] The weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is ≥45.

[0009] Preferably, in the slow-release oxidant, the weight ratio of polylactic acid, metal peroxide and citric acid is 1:2.5-2.7:1.7-1.8.

[0010] Preferably, the weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is 45-100.

[0011] Preferably, in the iron-based molecular sieve composite material, the weight content of Fe element is 3.2-4 wt%.

[0012] Preferably, the metal peroxide is selected from one or more of calcium peroxide, magnesium peroxide, and potassium peroxide.

[0013] Preferably, the method for preparing the slow-release oxidant includes: mixing polylactic acid with dichloromethane, then mixing it with metal peroxide and citric acid, then adding the mixed material dropwise into polytetrafluoroethylene powder to granulate, and then drying it.

[0014] Preferably, the preparation method of the iron-based molecular sieve composite material includes the following steps:

[0015] (1) Mix the organic iron source with the template agent, then add the organic silicon source dropwise into the mixture, and then age it.

[0016] (2) The aged material is subjected to hydrothermal reaction, then dried, and then the dried product is calcined.

[0017] Preferably, the organic iron source is ferric citrate;

[0018] Preferably, the template agent is tetrapropylammonium hydroxide;

[0019] Preferably, the organosilicon source is tetraethyl orthosilicate;

[0020] Preferably, the molar ratio of the organosilicon source, the organoiron source, and the template agent is 1:0.015-0.045:0.3-0.4, wherein the molar amount of the organosilicon source is SiO2 and the molar amount of the organoiron source is Fe2O3.

[0021] Preferably, the aging temperature is 20-30℃ and the aging time is 20-25h.

[0022] Preferably, the conditions for the hydrothermal reaction include: a temperature of 150-180℃ and a time of 60-90h.

[0023] Preferably, the calcination conditions include: a temperature of 500-600℃ and a time of 5-8 hours.

[0024] A second aspect of the present invention provides the application of the composition described herein in the removal of organic pollutants from groundwater;

[0025] Preferably, the organic pollutant in the groundwater is methyl tert-butyl ether.

[0026] A third aspect of the present invention provides a permeable reactive wall system for groundwater remediation, wherein the permeable reactive wall system comprises a slow-release material reactive wall and an adsorption reactive wall connected in sequence along the direction perpendicular to the groundwater flow direction.

[0027] The slow-release material reaction wall is filled with the above-mentioned composition;

[0028] The adsorption reaction wall is filled with the iron-based molecular sieve composite material from the above-mentioned composition.

[0029] A fourth aspect of the present invention provides a method for removing organic pollutants from groundwater, the method comprising: mixing and contacting the composition for groundwater remediation with groundwater containing organic pollutants;

[0030] Preferably, in the groundwater containing organic pollutants, the organic pollutant is methyl tert-butyl ether.

[0031] Preferably, in the groundwater containing organic pollutants, the concentration of the organic pollutants is 0.05 mmol / L to 2 mmol / L.

[0032] The iron-based molecular sieve composite material contained in the composition of this invention possesses both excellent adsorption performance and catalytic oxidation activity. The iron element in the composite material is uniformly dispersed and has a high loading capacity, allowing more active sites to be loaded onto the molecular sieve framework, further enhancing catalytic activity. Simultaneously, thanks to the structural stability of the molecular sieve framework, the iron-based molecular sieve composite material exhibits excellent adsorption and long-term stability, effectively achieving the adsorption and catalytic oxidation degradation of methyl tert-butyl ether in groundwater, and also possesses good reusability. Furthermore, in this invention, citric acid and metal peroxides are encapsulated in polylactic acid to construct a slow-release system, slowly releasing H2O2 and maintaining a certain concentration over a relatively long period to effectively degrade pollutants. Further, the citric acid contained in the slow-release oxidant of this invention can coordinate with metal ions to form complexes, promoting the Fe(III) / Fe(II) cycle, enhancing free radical generation, and further improving the performance of the iron-based molecular sieve composite material. Moreover, excess citric acid is decomposed by microorganisms in the water, preventing secondary pollution of the water body. Citric acid, a pH buffer, was used to further enhance the catalytic degradation of methyl tert-butyl ether by iron-based molecular sieves. A comprehensive remediation system combining slow-release oxidant and iron-based molecular sieve composite materials was constructed. This system not only improved the overall degradation performance of the materials but also enhanced the stability of groundwater remediation and the reusability of the materials, thus possessing broad application scenarios. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the preparation process of the iron-based molecular sieve composite material Fe-S-1-1 in Example 1;

[0034] Figure 2 This is a schematic diagram of the preparation process of the slow-release oxidant PLA@CP-CA in Preparation Example 10;

[0035] Figure 3 These are TEM images of the iron-based molecular sieve composite materials prepared in Preparation Examples 1, 5, and 7.

[0036] Figure 4 This is an elemental distribution diagram of Fe, Si, and O elements in the iron-based molecular sieve composite material prepared in Example 1;

[0037] Figure 5 Here are the SEM morphology and infrared images of PLA@CP-CA prepared in Example 10;

[0038] Figure 6 The images show the XRD patterns of the iron-based molecular sieve composite materials prepared in Examples 1-9.

[0039] Figure 7The images show the TG curves of the iron-based molecular sieve composite material Fe-S-1-1 prepared in Example 1 and the molecular sieve S-1 sample prepared in Comparative Example 1.

[0040] Figure 8 The results show the stability and repeatability of composition S1 as described in Example 1;

[0041] Figure 9 This is a schematic diagram of the experimental setup used in Test Example 6, which involves two treatment columns connected in series.

[0042] Figure 10 This is the test result graph for test example 6. Detailed Implementation

[0043] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] In this invention, the composition for groundwater remediation contains a slow-release oxidant and an iron-based molecular sieve composite material. The slow-release oxidant provides H₂O₂ for the catalytic reaction, while the iron-based molecular sieve composite material possesses both adsorption and catalytic oxidation functions. When remediating groundwater, it can be used simultaneously as an adsorbent and catalyst, adsorbing and catalytically oxidizing methyl tert-butyl ether (MTBE) in groundwater, achieving long-term removal of MTBE and thus groundwater remediation. The iron-based molecular sieve composite material also has a regeneration function. In practical applications, when used as an adsorbent, it does not need to be removed for regeneration; its adsorption performance is regenerated automatically, significantly reducing the operational costs of water remediation.

[0046] In this invention, the slow-release oxidant has a core-shell structure, with polylactic acid as the shell and metal peroxide and citric acid as the core. Metal peroxides can react with water to release H2O2 within a certain pH range. They are relatively stable, easy to transport, and can slowly release H2O2 using slow-release technology, maintaining a certain concentration for a relatively long time to effectively degrade pollutants. However, directly adding metal peroxides can cause a local pH increase in groundwater, and the hydroxides generated during the reaction can deposit on the surface of the metal peroxides, hindering their further dissolution. This results in the inability to effectively remove organic matter from groundwater in the long term, affecting the long-term stability of groundwater remediation. Adding a pH buffer during the preparation of the slow-release material is a strategy to control the pH changes caused by the metal peroxide reaction. However, the content of the pH buffer also has a certain impact on the heterogeneous reaction activity. Therefore, adding citric acid to the slow-release oxidant of this invention can lower the pH value of the solution, thereby inhibiting the formation of metal hydroxides and improving the long-term stability of the composition in groundwater remediation. On the other hand, citric acid can coordinate with metal ions to form complexes that promote the Fe(III) / Fe(II) cycle, enhance free radical generation, and further improve the performance of the iron-based molecular sieve composite material. Furthermore, excess citric acid will be decomposed by microorganisms in the water, preventing secondary pollution. Simultaneously, the polylactic acid coating also provides a slow-release effect, further enhancing the long-term stability of the composition.

[0047] In this invention, the iron-based molecular sieve composite material comprises a Silicalite-1 molecular sieve and Fe element supported on the Silicalite-1 molecular sieve. The Silicalite-1 molecular sieve is an all-silica type with an MFI topology. It possesses a microporous-mesoporous structure and highly dispersed metal sites, which can improve the aggregation phenomenon of nano-molecular sieves. Furthermore, it has strong surface hydrophobicity and a pore size similar to the kinetic diameter of methyl tert-butyl ether (MTBE), making it advantageous as a carrier material for the adsorption and removal of MTBE from aqueous solutions. In addition, the relatively large particle size of the Silicalite-1 molecular sieve allows for separation from aqueous solutions through filtration, making it suitable as an active reaction medium for permeable reaction walls. Loading Fe element onto the Silicalite-1 molecular sieve framework further enhances the dispersion of the catalytically active element Fe and increases the Fe loading, resulting in stronger catalytic activity and adsorption performance of the iron-based molecular sieve composite material. It also exhibits superior long-term stability, enabling long-term and efficient degradation of MTBE underground, thus better facilitating groundwater remediation.

[0048] In this invention, there is a strict dosage relationship between the slow-release oxidant and the iron-based molecular sieve composite material. The amount of the slow-release oxidant directly affects the removal rate of methyl tert-butyl ether (MTBE) in groundwater. The amount of the slow-release oxidant needs to be much greater than the amount of the iron-based molecular sieve composite material, and the weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material must be ≥45, meaning the amount of the slow-release oxidant is at least 45 times that of the iron-based molecular sieve composite material. A ratio lower than this limit will adversely affect the removal rate of MTBE in groundwater. More preferably, to further reduce the removal cost of MTBE in groundwater, the weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is limited to 45-100. Adding more slow-release oxidant in this range will not further improve the removal rate of MTBE but will instead increase the removal cost. Specifically, the weight ratio of the iron-based molecular sieve composite material to the slow-release oxidant can be 1:45, 1:50, 1:55, or 1:60.

[0049] In a preferred embodiment, the weight ratio of polylactic acid, metal peroxide and citric acid in the slow-release oxidant is 1:2.5-2.7:1.7-1.8, more preferably 1:2.6-2.64:1.74-1.75.

[0050] In this invention, the iron-based molecular sieve composite material has a high iron loading and uniform dispersion, which allows the composite material to expose more active sites when treating methyl tert-butyl ether (MTBE) in groundwater, thereby further improving the removal rate of MTBE. In the iron-based molecular sieve composite material, the Fe content is 3.2-4 wt%, preferably 3.4-3.7 wt%, and more preferably 3.5-3.6%. Specifically, the Fe content can be 3.2 wt%, 3.3 wt%, 3.4 wt%, 3.5 wt%, 3.54%, 3.6 wt%, 3.7 wt%, or 3.8 wt%. The Fe element in the iron-based molecular sieve composite material may exist in the form of iron oxide.

[0051] In a preferred embodiment, the metal peroxide is selected from one or more of calcium peroxide, magnesium peroxide, and potassium peroxide, preferably calcium peroxide.

[0052] In a preferred embodiment, the method for preparing the slow-release oxidant includes: mixing polylactic acid with dichloromethane, then mixing it with metal peroxide and citric acid, then adding the mixed material dropwise into polytetrafluoroethylene powder to granulate, and then drying it.

[0053] In a specific embodiment, polylactic acid is used as an encapsulating agent. In order to ensure that polylactic acid can better encapsulate metal peroxides and citric acid, the mixed material can be allowed to stand until it is semi-dry solid before being added to polytetrafluoroethylene powder for granulation. Then, the material is added to the polytetrafluoroethylene powder by a dropper for granulation. After drying, light yellow granules are obtained.

[0054] In a preferred embodiment, the weight ratio of polylactic acid, metal peroxide and citric acid is 1:2.5-2.7:1.7-1.8, preferably 1:2.55-2.65:1.7-1.75, and more preferably 1:2.6-2.64:1.74-1.75.

[0055] In a preferred embodiment, the preparation method of the iron-based molecular sieve composite material includes the following steps:

[0056] (1) Mix the organic iron source with the template agent, then add the organic silicon source dropwise into the mixture, and then age it.

[0057] (2) The aged material is subjected to hydrothermal reaction, then dried, and then the dried product is calcined.

[0058] Specifically, the dispersion and particle size of the active metal are crucial to the activity of iron-based molecular sieve composites. While impregnation with iron salts with high melting points can improve metal dispersion, it requires multiple steps, and the metal loading is difficult to guarantee. To further improve the activity of the composite material and load more active sites onto the molecular sieve framework, in the preparation process of the iron-based molecular sieve composite material of this invention, a metal precursor is directly added during the molecular sieve crystallization process, allowing the metal to enter the molecular sieve framework for loading during crystallization. However, since molecular sieves typically crystallize in a high-temperature, high-alkaline environment, the metal easily forms M(OH)3 precipitate, making it difficult to incorporate into the molecular sieve framework. Therefore, in a preferred embodiment of this invention, the organic iron source is ferric citrate. Citric acid, as a metal chelating agent, can significantly improve the stability of metal ions in solution and inhibit the precipitation and aggregation of metals during crystallization. The transition metal iron is introduced into the molecular sieve support via hydrothermal synthesis, ensuring both the iron loading and the dispersion of the active components, while simultaneously ensuring that the prepared iron-based molecular sieve composite material possesses excellent catalytic activity, catalytic stability, and adsorption performance.

[0059] In a preferred embodiment, the template agent is tetrapropylammonium hydroxide.

[0060] In a preferred embodiment, the organosilicon source is tetraethyl orthosilicate.

[0061] In a preferred embodiment, to further enhance the activity of the iron-based molecular sieve composite material, the molar ratio of the organosilicon source, the organoiron source, and the template agent is 1:0.015-0.045:0.3-0.4, wherein the molar amount of the organosilicon source is calculated as SiO2, and the molar amount of the organoiron source is calculated as Fe2O3. More preferably, the molar ratio of the organosilicon source, the organoiron source, and the template agent is 1:0.018-0.04:0.35-0.38, and more preferably, 1:0.018-0.035:0.35-0.38.

[0062] In a preferred embodiment, the aging temperature is 20-30℃, preferably 26-28℃, and the aging time is 20-25h, preferably 22-24h. Specifically, the aging temperature can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 28℃, or 30℃; and the aging time can be 20h, 22h, 24h, or 25h.

[0063] In a specific implementation, no precipitation occurred in the precursor solution during the aging stage in step (1), indicating that the chelation of iron ions by citric acid is beneficial to the stability of the metal and the dispersion and loading of the active metal.

[0064] In a specific embodiment, the aged solution undergoes a hydrothermal reaction to achieve product crystallization. Preferably, the conditions for the hydrothermal reaction include: a temperature of 150-180℃, more preferably 160-175℃, and a time of 60-90 hours, more preferably 65-85 hours, and even more preferably 70-80 hours. Specifically, the temperature of the hydrothermal reaction is 150℃, 160℃, 170℃, or 180℃; and the time of the hydrothermal reaction is 60 hours, 70 hours, 72 hours, 80 hours, 85 hours, or 90 hours.

[0065] In a specific implementation, the product after hydrothermal reaction is washed with water until the pH of the washing solution is 6.5-7.5, then the washed product is dried, and then the dried product is calcined to remove the template agent.

[0066] In a preferred embodiment, to ensure complete removal of the template agent from the product, the calcination temperature is 500-600℃, preferably 530-560℃, and more preferably 550℃; the calcination time is 5-8 hours, preferably 5.5-7 hours. Specifically, the calcination temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 580℃, or 600℃; the calcination time can be 5 hours, 6 hours, 7 hours, or 8 hours.

[0067] In a specific embodiment, the atmosphere during calcination is air.

[0068] This invention further provides the application of the aforementioned composition or the aforementioned permeable reactive barrier system for groundwater remediation in the removal of organic pollutants from groundwater. The composition of this invention can achieve highly efficient removal of various organic pollutants from groundwater, particularly the highly efficient degradation of methyl tert-butyl ether (MTBE), exhibiting both high efficiency and long-term stability. This effectively solves the current problem of the difficulty in degrading MTBE in groundwater, thus better facilitating groundwater remediation.

[0069] The present invention can also provide a permeable reactive barrier system for groundwater remediation. Perpendicular to the direction of groundwater flow, the permeable reactive barrier system includes a slow-release material reactive barrier and an adsorption reactive barrier connected in sequence. The slow-release material reactive barrier is used to slowly release H2O2, providing oxidizing substances for the subsequent adsorption reactive barrier. The adsorption reactive barrier is used to adsorb and catalytically oxidize and degrade organic pollutants to meet the final groundwater remediation standards.

[0070] In this invention, the filling medium in the slow-release material reaction wall is the composition for groundwater remediation described in this invention. The filling medium in the adsorption reaction wall can be selected from the iron-based molecular sieve composite material in the composition described in this invention as an adsorbent. The catalytic and adsorption properties of the iron-based molecular sieve composite material are used to efficiently remove methyl tert-butyl ether from groundwater.

[0071] The present invention also provides a method for removing organic pollutants from groundwater, the method comprising: mixing the composition for groundwater remediation of the present invention with groundwater containing organic pollutants and reacting the mixture.

[0072] In a specific embodiment, when the composition of the present invention is used for groundwater remediation, the composition can be used as a barrier medium to set up a permeable reactive barrier to remediate the groundwater. In a preferred embodiment, in the groundwater containing organic pollutants, the organic pollutant is methyl tert-butyl ether.

[0073] In a preferred embodiment, the composition of the present invention can degrade and remove high concentrations of organic pollutants in groundwater. The composition of the present invention can efficiently degrade and remove organic pollutants within a concentration range of 0.05 mmol / L to 2 mmol / L, exhibiting a high pollutant removal rate.

[0074] In a preferred embodiment, the reaction time is 7-9 hours. Specifically, the reaction time can be 7 hours, 8 hours, or 9 hours.

[0075] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0076] Preparation Example 1

[0077] A schematic diagram of the preparation process of the iron-based molecular sieve composite material Fe-S-1-1 is shown below. Figure 1 As shown, the specific method is as follows:

[0078] (1) Add ferric citrate to 3.02g of water, stir evenly, then add tetrapropylammonium hydroxide, stir at 25°C for 10min, then use a peristaltic pump to dropwise add tetraethyl orthosilicate to the mixture, and continue to stir and age at 25°C for 24h; wherein, the molar ratio of tetraethyl orthosilicate, ferric citrate and tetrapropylammonium hydroxide is 1:0.02:0.36, the molar amount of tetraethyl orthosilicate is calculated as SiO2, and the molar amount of ferric citrate is calculated as Fe2O3;

[0079] (2) The aged material was loaded into a hydrothermal reactor for hydrothermal reaction. The hydrothermal reaction temperature was 170℃ and the hydrothermal reaction time was 72h. After the reaction was completed, the temperature of the reactor was reduced to 25℃. Then the solid product was separated from the solution by centrifugation and the product was washed with deionized water until the pH value of the washing liquid was 7. Then the obtained product was placed in an oven and dried at 100℃ for 12h. Then the dried product was placed in a muffle furnace and calcined in air at 550℃ for 6h. After calcination, the iron-based molecular sieve composite material Fe-S-1-1 was obtained.

[0080] ICP testing revealed that the Fe content in the Fe-S-1-1 iron-based molecular sieve composite material was 3.54 wt%.

[0081] Preparation Example 2

[0082] Preparation of iron-based molecular sieve composite material Fe-S-1-2

[0083] The preparation method was carried out in accordance with Example 1, except that the molar ratio of tetraethyl orthosilicate, ferric citrate and tetrapropylammonium hydroxide was 1:0.04:0.36, the molar amount of tetraethyl orthosilicate was calculated as SiO2, and the molar amount of ferric citrate was calculated as Fe2O3.

[0084] ICP testing revealed that the Fe content in the Fe-S-1-2 iron-based molecular sieve composite material was 3.57%.

[0085] Preparation Example 3

[0086] Preparation of iron-based molecular sieve composite material Fe-S-1-3

[0087] The preparation method was carried out in accordance with Example 1, except that the molar ratio of tetraethyl orthosilicate, ferric citrate and tetrapropylammonium hydroxide was 1:0.01:0.36, the molar amount of tetraethyl orthosilicate was calculated as SiO2, and the molar amount of ferric citrate was calculated as Fe2O3.

[0088] ICP testing revealed that the Fe content in the Fe-S-1-3 iron-based molecular sieve composite material was 1.77%.

[0089] Preparation Example 4

[0090] Preparation of iron-based molecular sieve composite material Fe-S-1-4

[0091] The preparation method was carried out in accordance with the method of Preparation Example 1, except that the molar ratio of tetraethyl orthosilicate, ferric citrate and tetrapropylammonium hydroxide was 1:0.005:0.36, the molar amount of tetraethyl orthosilicate was calculated as SiO2, and the molar amount of ferric citrate was calculated as Fe2O3.

[0092] ICP testing revealed that the Fe content in the Fe-S-1-4 iron-based molecular sieve composite material was 0.87%.

[0093] Preparation Example 5

[0094] Preparation of iron-based molecular sieve composite material Fe-S-1-5

[0095] The procedure was carried out according to the method of Preparation Example 1, except that in step (2), the hydrothermal reaction time was 24 h.

[0096] ICP testing revealed that the Fe content in the iron-based molecular sieve composite material Fe-S-1-5 was 1.81%.

[0097] Preparation Example 6

[0098] Preparation of iron-based molecular sieve composite material Fe-S-1-6

[0099] The method of preparation example 1 was carried out, except that in step (2), the hydrothermal reaction time was 36 h.

[0100] ICP testing revealed that the Fe content in the Fe-S-1-6 iron-based molecular sieve composite material was 2.45%.

[0101] Preparation Example 7

[0102] Preparation of iron-based molecular sieve composite material Fe-S-1-7

[0103] The method of preparation example 1 was carried out, except that in step (2), the hydrothermal reaction time was 48 h.

[0104] ICP testing revealed that the Fe content in the Fe-S-1-7 iron-based molecular sieve composite material was 2.99%.

[0105] Preparation Example 8

[0106] Preparation of iron-based molecular sieve composite material Fe-S-1-8

[0107] The method of preparation example 1 was carried out, except that in step (2), the hydrothermal reaction time was 60 h.

[0108] ICP testing revealed that the Fe content in the Fe-S-1-8 iron-based molecular sieve composite material was 3.34%.

[0109] Preparation Example 9

[0110] Preparation of iron-based molecular sieve composite material Fe-S-1-9

[0111] The method of preparation example 1 was carried out, except that the hydrothermal reaction time in step (2) was 84 h.

[0112] ICP testing revealed that the Fe content in the Fe-S-1-9 iron-based molecular sieve composite material was 3.54%.

[0113] Preparation Example 10

[0114] A schematic diagram of the preparation process of the sustained-release oxidant PLA@CP-CA is shown below. Figure 2 As shown, the specific method is as follows:

[0115] 0.6734 g of polylactic acid (PLA) was used as an encapsulating agent and dissolved in 10 mL of dichloromethane. 1.7703 g of calcium peroxide and 1.1747 g of citric acid were weighed, mixed, and added to the PLA-dichloromethane solution. The mixture was then allowed to stand and evaporate to a semi-solid state. The material was then dropped onto polytetrafluoroethylene (PTFE) to granulate. The dichloromethane was then evaporated in an oven at 40 °C to obtain pale yellow PLA@CP-CA granules.

[0116] Example 1

[0117] Composition S1 for groundwater remediation consists of 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.15 g of slow-release oxidant PLA@CP-CA;

[0118] The method for using composition S1 for groundwater remediation to remove organic pollutants from groundwater is as follows:

[0119] First, a phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. In a centrifuge tube, 0.003 g of the iron-based molecular sieve composite material Fe-S-1-1 and 0.15 g of the slow-release oxidant PLA@CP-CA were added sequentially, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 hours. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na₂S₂O₃. Headspace gas chromatography was used to analyze the degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulation sample. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulation sample, which was 75.1%.

[0120] Example 2

[0121] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-2.

[0122] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was 74.6%.

[0123] Example 3

[0124] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-3.

[0125] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was found to be 62.6%.

[0126] Example 4

[0127] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-4.

[0128] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was 61.7%.

[0129] Example 5

[0130] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-5.

[0131] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was found to be 63.6%.

[0132] Example 6

[0133] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-6.

[0134] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was found to be 64.1%.

[0135] Example 7

[0136] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-7.

[0137] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was found to be 64.3%.

[0138] Example 8

[0139] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-8.

[0140] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was 70.2%.

[0141] Example 9

[0142] The experiment was carried out according to the method of Example 1, except that the iron-based molecular sieve composite material Fe-S-1-1 in composition S1 was replaced with an equal weight of iron-based molecular sieve composite material Fe-S-1-9.

[0143] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was 73.0%.

[0144] Example 10

[0145] The method of Example 1 was followed, except that the weight of the slow-release oxidant in composition S1 was 0.2 g.

[0146] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was 72.5%.

[0147] Example 11

[0148] Composition S2 for groundwater remediation consists of 0.003g of iron-based molecular sieve composite material Fe-S-1-1 and 0.33g of slow-release oxidant PLA@CP-CA;

[0149] The method for using composition S1 for groundwater remediation to remove organic pollutants from groundwater is as follows:

[0150] First, a phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. In a centrifuge tube, 0.003 g of the iron-based molecular sieve composite material Fe-S-1-1 and 0.33 g of the slow-release oxidant PLA@CP-CA were added sequentially, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 hours. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na₂S₂O₃. Headspace gas chromatography was used to analyze the degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulation sample. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulation sample to be 72.2%.

[0151] Comparative Example 1

[0152] The method of Example 1 was implemented, except that the composition S1 for groundwater remediation was replaced with composition D1.

[0153] The composition D1 consists of 0.003 g of molecular sieve S-1 and 0.15 g of slow-release oxidant PLA@CP-CA;

[0154] The molecular sieve S-1 is prepared as follows:

[0155] 7.65 g of tetrapropylammonium hydroxide was added to 10 g of water and stirred until homogeneous. Then, 5.36 g of tetraethyl orthosilicate was added dropwise to the solution using a peristaltic pump. The mixture was stirred at 25 °C for 24 h. The resulting material was then refluxed in an oil bath at 100 °C for 36 h. After the reaction was completed, the material was centrifuged (15000 rpm for 60 min, followed by ultrasonic dispersion for 20 min). The material was then washed with deionized water until the washing solution was neutral. The resulting product was then dried in an oven at 100 °C for 12 h. The dried product was then calcined in a muffle furnace in air at 550 °C for 6 h. After calcination, molecular sieve S-1 was obtained.

[0156] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples, which was found to be 11.6%.

[0157] Comparative Example 2

[0158] The method described in Example 1 is followed, except that the composition S1 for groundwater remediation does not contain the slow-release oxidant PLA@CP-CA.

[0159] The degradation degree of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples as 5.2%.

[0160] Comparative Example 3

[0161] The method of Example 1 was implemented, except that the composition S1 for groundwater remediation was replaced with composition D4.

[0162] Composition D4 for groundwater remediation consists of 0.003 g activated carbon and 0.15 g PLA@CP-CA;

[0163] The activated carbon is a commercially available product with a specific surface area of ​​500-1700 m². 2 / g.

[0164] The degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulated samples was analyzed using headspace gas chromatography (HGC). Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulated samples as 26.2%.

[0165] Comparative Example 4

[0166] Composition S2 for groundwater remediation consists of 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.105 g of slow-release oxidant PLA@CP-CA;

[0167] The method for using composition S1 for groundwater remediation to remove organic pollutants from groundwater is as follows:

[0168] First, a phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. In a centrifuge tube, 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.105 g of slow-release oxidant PLA@CP-CA were added sequentially, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 hours. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na₂S₂O₃. Headspace gas chromatography was used to analyze the degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulation sample. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulation sample, which was 58.5%.

[0169] Comparative Example 5

[0170] Composition S3 for groundwater remediation consists of 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.06 g of slow-release oxidant PLA@CP-CA;

[0171] The method for using composition S3 for groundwater remediation to remove organic pollutants from groundwater is as follows:

[0172] First, a phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. In a centrifuge tube, 0.003 g of the iron-based molecular sieve composite material Fe-S-1-1 and 0.06 g of the slow-release oxidant PLA@CP-CA were added sequentially, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 hours. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na₂S₂O₃. Headspace gas chromatography was used to analyze the degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulation sample. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulation sample, which was 55.8%.

[0173] Comparative Example 6

[0174] Composition S4 for groundwater remediation consists of 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.03 g of slow-release oxidant PLA@CP-CA;

[0175] The method for using composition S4 for groundwater remediation to remove organic pollutants from groundwater is as follows:

[0176] First, a phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. In a centrifuge tube, 0.003 g of iron-based molecular sieve composite material Fe-S-1-1 and 0.03 g of slow-release oxidant PLA@CP-CA were added sequentially, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 hours. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na₂S₂O₃. Headspace gas chromatography was used to analyze the degradation rate of methyl tert-butyl ether (MTBE) in the treated groundwater simulation sample. Three parallel experiments were conducted for each group, and the mean of the three parallel experiments was used to calculate the removal rate of MTBE in the groundwater simulation sample as 41.2%.

[0177] Test case

[0178] Test Example 1

[0179] The morphology of the iron-based molecular sieve composite materials prepared in Preparation Examples 1, 5, and 7 was tested using TEM, and the test results are as follows: Figure 3 As shown. Among them. Figure 3 a is a morphology diagram of the iron-based molecular sieve composite material prepared in Example 5. Figure 3 b is a morphology diagram of the iron-based molecular sieve composite material prepared in Example 7. Figure 3 c is a morphology diagram of the iron-based molecular sieve composite material prepared in Example 1. Figure 3 d is a partial magnified view of the iron-based molecular sieve composite material prepared in Example 1.

[0180] Depend on Figure 3 It can be seen that the iron-based molecular sieve composite material prepared by the present invention is a zeolite cluster formed by the aggregation of nano molecular sieves. As the hydrothermal crystallization time increases, the morphology of the iron-based molecular sieve composite material changes to a more regular spherical shape with a size of about 200 nm. It is fully crystallized and has a high degree of crystallinity.

[0181] The distribution of Fe, Si, and O elements in the iron-based molecular sieve composite material prepared in Example 1 was analyzed using STEM and EDS energy dispersive spectroscopy. The test results are as follows: Figure 4 As shown.

[0182] Depend on Figure 4 It can be seen that in the EDS energy dispersive spectroscopy surface scan mode, Fe element shows a strong signal, and Fe element is uniformly loaded on the framework of Silicalite-1 molecular sieve, and is highly dispersed on the Silicalite-1 molecular sieve framework with a high loading amount.

[0183] Test Example 2

[0184] The cross-sectional morphology of PLA@CP-CA prepared in Example 10 was tested using SEM, and the test results are as follows: Figure 5 As shown in a.

[0185] like Figure 5 As shown in Figure a, the interface of the PLA@CP-CA cross-section exhibits an irregular and rough morphology, with relatively uniform and dispersed particle distribution and no obvious uncrosslinked particles. This indicates that PLA is uniformly mixed with CP and CA and fully embedded, without any clumping or caking.

[0186] In addition, FTIR analysis was performed on PLA@CP-CA, polylactic acid (PLA), calcium peroxide (CP), and citric acid (CA) prepared in Preparation Example 10. The results are as follows: Figure 5 As shown in b.

[0187] Depend on Figure 5 b indicates that PLA@CP-CA is at 1194cm.–1 1130cm –1 and 1093cm –1 There are still 3 obvious -CO- stretching vibration peaks, which proves that the cross-linking effect inside the material is obvious, and polylactic acid can fully encapsulate calcium peroxide and citric acid.

[0188] Test Example 3

[0189] The iron-based molecular sieve composite materials prepared in Examples 1-9 were analyzed and tested using XRD, and the results are as follows: Figure 6 As shown.

[0190] according to Figure 6 The results of a show that the hydrothermal crystallization time during the preparation process has a significant impact on the crystallinity of the product, and the crystallinity of the sample increases with the extension of the crystallization time.

[0191] in addition, Figure 6 b shows that products with different silicon-iron ratios added during the preparation process all exhibit diffraction peaks of MFI-type molecular sieves, but no obvious diffraction peaks of iron oxide. However, when the ratio of silicon to iron in the raw materials increases (i.e., when the amount of iron added gradually increases), the intensity of the XRD diffraction peaks decreases. The incorporation of iron may affect the state of silicon species, especially the degree of crystallinity in the system. This indicates that in the preparation method described in this invention, the limited hydrothermal crystallization time and the ratio of raw materials have a certain impact on the crystallinity and configuration of the product. Furthermore, the iron-based molecular sieve composite material prepared under the preparation conditions specified in this invention has higher crystallinity and more excellent catalytic activity and adsorption performance.

[0192] Test Example 4

[0193] The thermal stability of the iron-based molecular sieve composite material Fe-S-1-1 prepared in Preparation Example 1 and the molecular sieve S-1 sample prepared in Comparative Example 1 were analyzed using a simultaneous thermal analyzer (METTLER TOLEDO TGA / DSC1 / 1600LF). Test conditions: Under air atmosphere (flow rate 10 mL / min), the temperature was increased from room temperature to 900℃ at a rate of 10℃ / min. The results are as follows: Figure 7 As shown.

[0194] Depend on Figure 7 It can be seen that although the morphology of the iron-based molecular sieve composite material Fe-S-1-1 synthesized in situ by hydrothermal method has changed, it still has excellent thermal stability and is not much different from S-1. It still maintains a low weight loss rate at a high temperature of 900℃.

[0195] Test Example 5

[0196] The reusability of the iron-based molecular sieve composite material in the composition for groundwater remediation was tested using the following method: A phosphate buffer solution with pH=7 was prepared, and MTBE was added to prepare a groundwater simulation sample with an MTBE concentration of 0.1 mmol / L. The sample was then stored at 4°C. 0.023 g of the iron-based molecular sieve composite material Fe-S-1-1 and 1.12 g of the slow-release oxidant PLA@CP-CA were added sequentially to a centrifuge tube, followed by 15 mL of the groundwater simulation sample. The mixture was then placed in a constant-temperature shaker and reacted at 25°C and 200 rpm for 8 h. After centrifugation, the sample was treated with 100 μL of 1 mol / L Na2S2O3, and the degradation degree of methyl tert-butyl ether in the simulated wastewater was analyzed by headspace gas chromatography. The reacted iron-based molecular sieve composite material Fe-S-1-1 was then centrifuged and dried overnight at 60°C. It was then mixed with fresh slow-release oxidant PLA@CP-CA, and the degradation test of MTBE in the aqueous solution was repeated. The test results are shown below. Figure 8 As shown in a.

[0197] Depend on Figure 8 As can be seen from this, most of the active iron species in the iron-based molecular sieve composite material of the composition of the present invention are located in the molecular sieve framework or encapsulated in the channels, which inhibits the loss of active components during the reaction process and significantly improves the reusability of the iron-based molecular sieve composite material. It can still maintain a 100% removal rate of MTBE during 8 reuses and has excellent long-term stability.

[0198] The concentration of iron ions leached from the iron-based molecular sieve composite material in water during repeated degradation was determined using ICP. The results are as follows: Figure 8 As shown in b. From Figure 8 As can be seen from b, the iron-based molecular sieve composite material prepared by the present invention has only a small amount of iron ions leaching out during repeated use, which is lower than the iron ion content standard of groundwater IV (2.0 mg / L). This firstly ensures the repeatability of its activity, and further illustrates that the composition described in the present invention will not cause secondary pollution to groundwater when it is used for groundwater remediation, and can achieve the purpose of efficient degradation and green remediation of groundwater.

[0199] Test Example 6

[0200] The composition was tested as a permeable reactive barrier to assess its degradation of MTBE in groundwater.

[0201] Test group: A simulation study of PRB (permeable reactive barrier) experiments was conducted using two layers of treatment columns connected in series. A schematic diagram of the experimental setup is shown below. Figure 9As shown, the multi-channel constant flow pump is the water supply device. Both the slow-release material column and the adsorption material column used in the experiment were filled with plexiglass columns, each 80 mm high, 20 mm inner diameter, and 30 mm outer diameter. The first column was the slow-release material column, and the second column was the adsorption material column. First, a 20 mm thick layer of 16-30 mesh quartz sand was laid at the bottom of both columns. Then, a 40 mm thick layer of the slow-release oxidant PLA@CP-CA was filled into the slow-release material column, and a 40 mm thick layer of iron-based molecular sieve composite material Fe-S-1-1 was filled into the adsorption material column. Finally, a 20 mm thick layer of 16-30 mesh quartz sand was laid on top. The inert quartz sand was placed at both ends of the column to simulate the intermediate layer of groundwater and soil, ensuring the stability of the water flow.

[0202] Control group: Only one adsorption column was set up, and the adsorption column was filled with activated carbon material (commercially available);

[0203] Test Procedure: Simulated groundwater (MTBE concentration of 10 mg / L) was injected into the slow-release oxidation column of the test group and the adsorption column of the control group using a constant flow pump, with the flow rate controlled at 1 mL / min. The experiment was conducted at room temperature (25℃) and the entire simulated PRB experiment was maintained for 200 h. Groundwater samples were periodically taken from the outlet of the second adsorption column in the test group and the adsorption column in the control group for analysis. Headspace chromatography was used to analyze the concentration changes of MTBE and TBA (tert-butanol, an intermediate product of MTBE degradation) in the treated water samples. The test results are shown in Figure 10a. Simultaneously, ICP was used to test the Fe ion concentration in the water samples, and the test results are shown in Figure 10a. Figure 10 As shown in b.

[0204] The headspace sampler was kept at 65°C for 20 min; the sample flow path temperature was 90°C; and the transfer line temperature was 105°C. The injection port temperature was 220°C, the split ratio was 1:10, a flame ionization detector (FID) was used at 260°C, a DB-624 capillary column was used, helium was used as the carrier gas, and the column flow rate was 10 mL / min. The column oven temperature program was 40°C for 2 min, then increased to 120°C at 10°C / min and held for 3 min. Sample concentration was determined using the external standard method.

[0205] Depend on Figure 10 As can be seen from a, the composition described in this invention, as a permeable reactive barrier, can significantly reduce the concentration of MTBE in groundwater and can also achieve in-situ degradation of the intermediate product TBA, with a long degradation time. Its performance is superior to that of the commonly used single-layer adsorption column (control group) in the prior art. Furthermore, according to… Figure 10The results in b show that the iron-based molecular sieve composite material used in this invention can still maintain the stability of its structure during use, and the iron element it loads can still be completely preserved under dynamic water flow. After use, it will not generate a large amount of iron sludge, causing secondary pollution to the environment, and has broad application prospects.

[0206] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for groundwater remediation, characterized in that, The composition contains a slow-release oxidant and an iron-based molecular sieve composite material; The slow-release oxidant has a core-shell structure, with the shell being polylactic acid and the core being a metal peroxide and citric acid; The iron-based molecular sieve composite material contains Silicalite-1 molecular sieve and Fe element supported on Silicalite-1 molecular sieve; The weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is ≥45.

2. The composition according to claim 1, characterized in that, In the slow-release oxidant, the weight ratio of polylactic acid, metal peroxide, and citric acid is 1:2.5-2.7:1.7-1.8; and / or The weight ratio of the slow-release oxidant to the iron-based molecular sieve composite material is 45-100.

3. The composition according to claim 1, characterized in that, In the iron-based molecular sieve composite material, the weight content of Fe element is 3.2-4 wt%.

4. The composition according to claim 1 or 2, characterized in that, The metal peroxide is selected from one or more of calcium peroxide, magnesium peroxide, and potassium peroxide.

5. The composition according to any one of claims 1-4, characterized in that, The method for preparing the slow-release oxidant includes: mixing polylactic acid with dichloromethane, then mixing it with metal peroxide and citric acid, then adding the mixed material dropwise into polytetrafluoroethylene powder to granulate, and then drying it.

6. The composition according to any one of claims 1-4, characterized in that, The preparation method of the iron-based molecular sieve composite material includes the following steps: (1) Mix the organic iron source with the template agent, then add the organic silicon source dropwise into the mixture, and then age it. (2) The aged material is subjected to hydrothermal reaction, then dried, and then the dried product is calcined.

7. The composition according to claim 6, characterized in that, The organic iron source is ferric citrate; Preferably, the template agent is tetrapropylammonium hydroxide; Preferably, the organosilicon source is tetraethyl orthosilicate; Preferably, the molar ratio of the organosilicon source, the organoiron source, and the template agent is 1:0.015-0.045:0.3-0.4, wherein the molar amount of the organosilicon source is SiO2 and the molar amount of the organoiron source is Fe2O3.

8. The composition according to claim 6, characterized in that, The aging temperature is 20-30℃, and the aging time is 20-25h.

9. The composition according to claim 6, characterized in that, The conditions for the hydrothermal reaction include: a temperature of 150-180℃ and a time of 60-90h.

10. The composition according to claim 6, characterized in that, The calcination conditions include a temperature of 500-600℃ and a time of 5-8 hours.

11. The use of the composition according to any one of claims 1-10 in the removal of organic pollutants from groundwater; Preferably, the organic pollutant in the groundwater is methyl tert-butyl ether.

12. A permeable reactive barrier system for groundwater remediation, characterized in that, In the direction perpendicular to the flow direction of groundwater, the permeable reactive wall system includes a slow-release material reactive wall and an adsorption reactive wall connected in sequence. The slow-release material reaction wall is filled with the composition according to any one of claims 1-10; The adsorption reaction wall is filled with the iron-based molecular sieve composite material of any one of claims 1-10.

13. A method for removing organic pollutants from groundwater, characterized in that, The method includes: mixing and contacting a composition for groundwater remediation with groundwater containing organic pollutants; The composition for groundwater remediation is the composition according to any one of claims 1-10; Preferably, in the groundwater containing organic pollutants, the organic pollutant is methyl tert-butyl ether.

14. The method according to claim 13, characterized in that, In the groundwater containing organic pollutants, the concentration of the organic pollutants is 0.05 mmol / L to 2 mmol / L.

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