Floating type slow-release persulfate oxidation material and preparation method and application thereof

Abstract

This application relates to the field of groundwater pollution remediation technology, and discloses a floating slow-release persulfate oxidation material, its preparation method, and its application. The floating slow-release persulfate oxidation material includes: a paraffin shell, a cylindrical closed structure, used to provide hydrophobic buoyancy and physical isolation; release holes are opened on both ends of the paraffin shell, serving as channels for external water to enter; and an inner core, filled inside the paraffin shell, composed of a dry powder matrix of hydroxypropyl methylcellulose and persulfate; wherein, after absorbing water, the inner core forms a gel network to inhibit the dissolution and diffusion rate of persulfate. The technical solution provided by this application can simultaneously achieve low-density floating positioning and precise long-term controlled release based on preset microchannels, meeting the synergistic requirements of targeted deployment, adjustable cycle, and stability for several months in in-situ remediation of petrochemical-confined sites using LNAPL.

Description

Technical Field

[0001] This application relates to the field of groundwater pollution remediation technology, and in particular to a floating slow-release persulfate oxidizing material, its preparation method and application. Background Technology

[0002] When petrochemical enterprises implement in-situ chemical oxidation remediation in restricted sites, they face multiple constraints such as dense equipment, complex pipelines, short construction windows, dispersed remediation areas, and long cycles. This requires persulfate slow-release materials to have three core capabilities: long-term stable release, precise and controllable release, and targeted dosing. However, there is a significant mismatch between existing mainstream slow-release materials and the needs: double-layer cement-based slow-release materials have high density and are prone to sinking, making them unsuitable for surface oil remediation; release control relies on permeability coefficient adjustment, which is a crude method and inconvenient for construction in confined spaces; paraffin-based slow-release candles have the risk of initial explosive release, release rate is affected by the randomness of porosity and cannot be accurately predicted, and are prone to structural collapse in long-term complex water and soil environments, making it difficult to maintain release stability for several months. Therefore, ideal persulfate slow-release materials need to break through the existing technical framework, adopt a low-density, high-mechanical-strength composite material structure, abandon the release mechanism that relies on the overall substrate permeability, and achieve modular production with rapid curing without molds.

[0003] Therefore, how to develop a persulfate slow-release material that can simultaneously achieve low-density floating positioning and precise long-term controlled release based on preset microchannels, in order to meet the synergistic requirements of LNAPL in-situ remediation in petrochemical-restricted sites for targeted deployment, adjustable cycle, and stability over several months, is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] This application provides a floating slow-release persulfate oxidizing material, its preparation method, and its application. It achieves the technical effect of simultaneously realizing low-density floating positioning and precise long-term controlled release based on preset microchannels, so as to meet the synergistic requirements of fixed-point delivery, adjustable cycle, and stability for several months for LNAPL in-situ remediation in petrochemical-restricted sites.

[0005] To achieve the above objectives, the main technical solutions adopted in this application include: In a first aspect, embodiments of this application provide a floating, slow-release persulfate oxidation material, comprising: The paraffin shell has a cylindrical, closed structure to provide hydrophobic buoyancy and physical isolation; release holes are provided on both ends of the paraffin shell, which serve as channels for external water to enter. The inner core, which fills the interior of the paraffin shell, is composed of a dry powder matrix made of a mixture of hydroxypropyl methylcellulose and persulfate. The inner core forms a gel network after absorbing water, which is used to inhibit the dissolution and diffusion rate of persulfate.

[0006] In one embodiment, the viscosity of the hydroxypropyl methylcellulose is 80,000-120,000 mPa•s.

[0007] In one embodiment, the mass ratio of the hydroxypropyl methylcellulose to the persulfate is 1:1 to 2:1.

[0008] In one embodiment, the persulfate is one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0009] In one embodiment, the number of release holes on each end face is 2-5, and the diameter of each release hole is 0.2-0.5 mm.

[0010] In one embodiment, the particle size of the dry powder matrix is ​​less than or equal to 100 mesh.

[0011] Secondly, embodiments of this application provide a method for preparing a floating, slow-release persulfate oxidizing material, the method comprising: Molten paraffin wax is poured into a mold, cooled and solidified, and then demolded to obtain a paraffin wax shell closed at one end. Weigh out hydroxypropyl methylcellulose and persulfate according to the mass ratio, mix them evenly to obtain a mixed powder; The mixed powder is compacted into the interior of the paraffin shell, and the other end is sealed with molten paraffin. Using a heated needle, vertically puncture both ends of the paraffin shell to form release holes.

[0012] In one embodiment, the compact filler has a fill rate greater than or equal to 80%.

[0013] Thirdly, this application provides an application of a floating slow-release persulfate oxidizing material. The floating slow-release persulfate oxidizing material described above or the floating slow-release persulfate oxidizing material prepared by the above preparation method is applied to shallow groundwater accumulation areas or non-aqueous liquid contamination layers. The floating slow-release persulfate oxidizing material utilizes the hydrophobicity of the paraffin shell to float on the surface of the water, so that the sulfate free radicals released by the floating slow-release persulfate oxidizing material are in the same spatial position as the floating petroleum hydrocarbon pollutants, so as to provide on-site oxidation and remediation.

[0014] In one embodiment, the release time of the floating slow-release persulfate oxidizing material is greater than 150 days.

[0015] The technical solution provided by one or more embodiments of this application achieves stable floating on the surface of shallow groundwater through the hydrophobic buoyancy of the paraffin shell, enabling precise contact with floating petroleum hydrocarbon (LNAPL) contamination layers. This solves the problem that traditional oxidants, due to their greater density than water, sink to the bottom and cannot effectively contact floating pollutants. Simultaneously, the strong hydrophobicity and chemical inertness of paraffin form the first physical barrier, completely isolating the external water body from direct, large-area contact with the internal persulfate, fundamentally eliminating the risk of explosive release due to the immediate solubility of traditional granular oxidants upon water contact. Furthermore, the design of release holes on both ends of the paraffin shell forcibly transforms three-dimensional surface contact release into one-dimensional pore diffusion release, significantly reducing the mass exchange rate. The gel network formed by the hydroxypropyl methylcellulose in the inner core after absorbing water further increases the resistance to the outward diffusion of persulfate ions, achieving a shift from dissolution control to diffusion control, ensuring the stability and long-term effectiveness of the release curve. In summary, this material combines multiple technical advantages, including precise targeting, anti-sudden release, controllable sustained release, and high utilization rate. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A cross-sectional view of a floating slow-release persulfate oxidizing material provided in an embodiment of this application; Figure 2 This is a cross-sectional view of the overall structure of the floating slow-release persulfate oxidizing material provided in the embodiments of this application; Figure 3 This is a schematic diagram of the release mechanism provided in the embodiments of this application; Figure 4 A flowchart illustrating a method for preparing a floating, slow-release persulfate oxidizing material, as provided in this application embodiment; Figure 5 This is a test diagram illustrating the effect of different numbers of release pores on persulfate release performance, provided in an embodiment of this application. Figure 6 This diagram illustrates the effect of different coating structures on the sustained-release performance of persulfate, as provided in the embodiments of this application. Figure 7 The graph shows the effect of different mixing ratios of HPMC and persulfate on release performance in the embodiments of this application. Figure 8 The graph shows the effect of different viscosity grades of HPMC on the sustained-release performance of persulfate, as provided in the embodiments of this application.

[0017] Explanation of reference numerals in the attached figures 1-Paraffin shell, 2-Inner core, 3-Release hole. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Implementing in-situ chemical oxidation remediation in restricted areas of petrochemical enterprises faces multiple challenges, including dense equipment, complex pipelines, short construction windows, and dispersed remediation areas with long required cycles. To address these constraints, persulfate slow-release materials must possess three core capabilities: first, long-term stable release, maintaining continuous oxidation capacity for months or even longer after a single application; second, precise and controllable release, with a predictable and adjustable release rate to adapt to different remediation cycles, avoiding persulfate waste or safety risks; and third, targeted application, requiring the material to float or remain stably in shallow groundwater / oil slick areas to ensure that the oxidant and LNAPL contaminants are at the same level of action and are not lost in water flow.

[0020] However, the design intent of existing mainstream slow-release materials is significantly mismatched with the aforementioned stringent requirements. For example, while double-layer cement-based slow-release materials can achieve long-term release, their high density causes them to sink to the bottom, making them unsuitable for surface oil remediation. Their release regulation relies on permeability coefficient adjustments, a crude method that is difficult to adapt quickly to varying timeframes. Furthermore, their molding and cement curing processes are inconvenient to implement in confined spaces. Another type of paraffin-based slow-release candle, while capable of floating, faces a high risk of initial "explosive release." The release rate is unpredictable due to the randomness of paraffin porosity, and the paraffin-fly ash composite structure is prone to porosity evolution or structural collapse in long-term complex water and soil environments, making it difficult to guarantee release stability for months.

[0021] Therefore, to meet the specific needs of petrochemical-restricted sites, ideal persulfate slow-release materials need to break through the existing technological framework: structurally, they should adopt low-density, high-mechanical-strength composite materials to ensure floating positioning and resistance to water erosion; in terms of release mechanism, the model relying on the overall substrate permeability should be abandoned; and in terms of workability, modular production that is mold-free and rapidly curing should be achieved to adapt to flexible deployment in dispersed areas.

[0022] In summary, the urgent technical problem to be solved is how to develop a persulfate slow-release material that can simultaneously achieve low-density floating positioning and precise long-term controlled release based on pre-set microchannels, so as to meet the synergistic requirements of LNAPL in-situ remediation in petrochemical-restricted sites for targeted deployment, adjustable cycle, and stability for several months.

[0023] To address the aforementioned technical problems, this application provides a floating, slow-release persulfate oxidation material. Figure 1 Cross-sectional view of the floating slow-release persulfate oxidizing material provided in the embodiments of this application and Figure 2 A cross-sectional view of the overall structure of the floating slow-release persulfate oxidizing material provided in the embodiments of this application includes: The paraffin shell 1 has a cylindrical closed structure, which is used to provide hydrophobic buoyancy and physical isolation; release holes 3 are opened on both ends of the paraffin shell 1, which serve as channels for external water to enter. The inner core 2, which is filled inside the paraffin shell 1, is composed of a dry powder matrix made of a mixture of hydroxypropyl methylcellulose and persulfate; The inner core 2 forms a gel network after absorbing water, which is used to inhibit the dissolution and diffusion rate of persulfate.

[0024] Specifically, paraffin wax not only has a lower density than water, providing sufficient buoyancy to allow the material to float stably on the surface of shallow groundwater, precisely targeting floating petroleum hydrocarbon (LNAPL) contaminants; more importantly, paraffin wax possesses extremely strong hydrophobicity and chemical inertness. This forms the first physical barrier, completely isolating the external water body from direct, large-area contact with the internal oxidant (persulfate), fundamentally eliminating the risk of explosive release that occurs when traditional granular oxidants dissolve immediately upon entering water.

[0025] The release holes 3 on both ends of the paraffin shell 1 are the only channels for external moisture to enter and for the dry powder matrix inside to be released. This structural design forces the three-dimensional surface contact release into a one-dimensional pore diffusion release, which greatly reduces the rate of material exchange.

[0026] The inner core 2 is physically mixed with hydroxypropyl methylcellulose (HPMC) and persulfate powder. When a small amount of water seeps into the inner core 2 through the release pores, the hydrophilic HPMC rapidly absorbs water and swells, forming a dense, high-viscosity gel network inside the pores. This gel acts like a soft plug, greatly increasing the resistance to the outward diffusion of persulfate ions. Persulfate must pass through this gel network to be released, thus achieving a shift from dissolution-controlled to diffusion-controlled release and ensuring a stable release profile. For a detailed release mechanism, please refer to [link to relevant documentation]. Figure 3 This is a schematic diagram of the release mechanism provided in the embodiments of this application. The persulfate in the schematic diagram is potassium persulfate as an example.

[0027] Preferably, the viscosity of hydroxypropyl methylcellulose is 80,000-120,000 mPa•s.

[0028] Specifically, if the viscosity of HPMC is below 80,000 mPa•s (such as common low-viscosity models), the gel strength formed after water absorption is insufficient, and the low viscosity cannot effectively inhibit the rapid dissolution and diffusion of persulfate, easily leading to excessively high initial concentrations (burst release). Furthermore, the gel layer is easily washed away and destroyed by water flow, making it impossible to maintain long-term release. If the viscosity is too high, the formed gel layer is too dense and hard, which may prevent persulfate from diffusing effectively at all, forming a dead core phenomenon, resulting in extremely low material utilization.

[0029] Therefore, 80,000-120,000 mPa•s is the optimal range for balancing sustained-release stability and persulfate release efficiency.

[0030] Preferably, the mass ratio of hydroxypropyl methylcellulose to persulfate is 1:1 to 2:1.

[0031] Specifically, a 1:1 mass ratio with a high persulfate content provides sufficient total remediation; meanwhile, the HPMC content is sufficient to form a continuous gel network. Increasing the HPMC ratio (2:1) results in a denser gel network, further extending the sustained-release time and enhancing safety, making it suitable for scenarios requiring extremely long release cycles but with relatively low pollution loads.

[0032] In addition, if the persulfate ratio is too high (exceeding 1:1), the gel network is insufficient, and the inner core 2 is prone to disintegration or rapid erosion after contact with water, thus losing its slow-release function; if the HPMC ratio is too high (exceeding 2:1), the persulfate content is too low, the repair efficiency drops significantly, and the material cost increases.

[0033] Preferably, the persulfate is one of potassium persulfate, ammonium persulfate, or sodium persulfate.

[0034] Specifically, potassium persulfate, ammonium persulfate, and sodium persulfate are all common strong oxidizing agents and water-soluble salts. The sustained-release mechanism in this embodiment relies on the gelation retardation effect of HPMC and is independent of the specific cation type of the persulfate. Therefore, this technical solution is universally applicable to all three salts and can produce the same sustained-release effect.

[0035] Preferably, the number of release holes on each end face is 2-5, and the diameter of each release hole is 0.2-0.5mm.

[0036] Specifically, when the pore size is less than 0.2 mm, the pores are easily blocked by the cooling and shrinkage of paraffin or impurities, and the diffusion flux is too small, resulting in low repair efficiency; when the pore size is greater than 0.5 mm, the water inflow rate is too fast, and HPMC does not have time to form a dense gel sealing layer at the pore opening, which will cause the inner core 2 to be flooded, leading to rapid loss and sudden release of persulfate.

[0037] Two to five release holes per end face provide a suitable total diffusion cross-sectional area. Too few holes result in slow release, while too many holes weaken the structural strength of the paraffin shell and may lead to an excessively fast and uncontrollable release rate.

[0038] Preferably, the particle size of the dry powder matrix is ​​less than or equal to 100 mesh.

[0039] Specifically, the particle size of the powder directly affects the filling density and uniformity of the core. A particle size of 100 mesh or less ensures that the gaps between the dry powder matrix particles are small during filling, allowing for compact filling. This helps to form a uniform, crack-free gel network after water absorption, avoiding the formation of internal macroscopic channels caused by the accumulation of large particles (i.e., water flows directly through large gaps without being blocked by the gel), thus ensuring the predictability and stability of the release rate.

[0040] This embodiment provides a floating, slow-release persulfate oxidizing material that achieves stable buoyancy on shallow groundwater surfaces through the hydrophobic buoyancy of its paraffin shell. This allows for precise targeting of floating petroleum hydrocarbon (LNAPL) contamination layers, solving the problem of traditional oxidants sinking to the bottom due to their higher density than water and their inability to effectively contact floating pollutants. Simultaneously, the strong hydrophobicity and chemical inertness of paraffin form the first physical barrier, completely isolating the external water from direct, large-area contact with the internal persulfate, fundamentally eliminating the risk of explosive release due to the immediate solubility of traditional granular oxidants upon water exposure. Furthermore, the release pores on both ends of the paraffin shell forcibly transform the three-dimensional surface contact release into a one-dimensional pore diffusion release, significantly reducing the mass exchange rate. The gel network formed by the hydroxypropyl methylcellulose in the core after absorbing water further increases the resistance to the outward diffusion of persulfate ions, achieving a shift from dissolution control to diffusion control, ensuring a stable and long-lasting release curve. In summary, this material combines multiple technical advantages, including precise targeting, anti-sudden release, controllable slow release, and high utilization rate.

[0041] This application also provides a method for preparing a floating, slow-release persulfate oxidizing material. Figure 4 A flowchart illustrating a method for preparing a floating, slow-release persulfate oxidizing material provided in this application embodiment is shown below. Figure 4 As shown, the preparation method includes the following steps: Step S1: Molten paraffin wax is injected into a mold, cooled and solidified, and then demolded to obtain a paraffin wax shell closed at one end; Step S3: Weigh hydroxypropyl methylcellulose and persulfate according to the mass ratio, mix them evenly, and obtain a mixed powder; Step S5: Compactly fill the inside of the paraffin shell with the mixed powder, and seal the other end with molten paraffin. Step S7: Using a heated needle, vertically pierce both ends of the paraffin shell to form release holes.

[0042] Specifically, molten paraffin wax (preferably fully refined paraffin wax with a melting point of 52-54°C) is injected into a mold and cooled to obtain a cylindrical container with uniform wall thickness and a dense structure. The closed-end design facilitates the subsequent filling of the inner core powder mixture. This formed paraffin shell not only provides the material with hydrophobicity and buoyancy but also serves as the first physical barrier to isolate external water from the internal powder mixture.

[0043] Weigh out hydroxypropyl methylcellulose (HPMC) and persulfate at a specific mass ratio (e.g., 1:1 or 2:1) and mix thoroughly. This step physically premixes the oxidant and the slow-release matrix material at the microscale. Ensuring uniform mixing is crucial to guarantee that during subsequent water absorption, each HPMC will swell synchronously to form a gel, preventing rapid dissolution caused by excessively high local persulfate concentrations.

[0044] The mixed powder is filled into the interior of the paraffin shell and sealed with molten paraffin. This step has two key functions: Sealing: The mixed powder is completely sealed inside the paraffin shell, eliminating any possibility of side leakage except for the micropores to be drilled at both ends.

[0045] Compact filling: Compact filling has a fill ratio of 80% or higher. High fill ratio means that the gaps between the mixed powder particles are extremely small, resulting in a dense structure. If the filling is loose, the core is prone to disintegration after water enters, or large water flow channels are formed inside (i.e., water flows away directly without passing through the gel barrier), leading to the failure of slow release. Compact filling ensures that a uniform and dense overall gel network is formed after water absorption.

[0046] By vertically piercing both ends with a heated needle, the paraffin wax at the contact point melts instantly. After the needle is withdrawn, the surrounding paraffin wax rapidly cools and shrinks. This hot-melt-cold-shrink mechanism naturally forms micropores with smooth edges, precise dimensions (0.2-0.5 mm), and dense, burr-free pore walls. Compared to mechanical drilling at room temperature, heated needle piercing does not produce paraffin debris, effectively preventing debris from falling into the shell and clogging persulfate or blocking the pores, ensuring absolutely unobstructed release channels.

[0047] This embodiment provides a method for preparing a floating, slow-release persulfate oxide material. By injecting molten paraffin into a mold and cooling it to solidify, a cylindrical paraffin shell with uniform wall thickness and a dense structure is obtained. The closed-end design facilitates subsequent core filling. Simultaneously, the paraffin shell itself provides the material with hydrophobic buoyancy and serves as the first physical barrier against external water. By premixing hydroxypropyl methylcellulose (HPMC) and persulfate at a specific mass ratio at the microscale, uniform mixing is ensured. This allows the HPMC to swell synchronously throughout the material during subsequent water absorption, forming a gel network and preventing localized excessive persulfate concentrations. The rapid dissolution caused by high temperatures is prevented by tightly filling the paraffin shell with mixed powder and sealing it with molten paraffin, thus eliminating the possibility of side leakage. This also avoids the problem of core disintegration or the formation of large water channels due to loose filling, ensuring a uniform and dense overall gel network after water absorption. Finally, the hot-melt-cold-shrinkage mechanism of vertically piercing both ends with a heated needle naturally forms micropores with smooth edges and precise dimensions. Compared to room-temperature mechanical drilling, this effectively avoids paraffin debris falling into the shell and clogging the persulfate or blocking the channels, ensuring absolutely unobstructed release channels. In summary, this preparation method is simple, convenient, and can efficiently prepare floating, slow-release persulfate oxide materials with excellent properties such as precise targeting, anti-sudden release, controllable sustained release, and high utilization rate.

[0048] This application also provides an application of a floating slow-release persulfate oxidizing material. The above-mentioned floating slow-release persulfate oxidizing material or the floating slow-release persulfate oxidizing material prepared by the above preparation method is applied to shallow groundwater accumulation areas or non-aqueous liquid pollution layers. In this application, the floating slow-release persulfate oxidizing material floats on the water surface due to the hydrophobicity of the paraffin shell, so that the sulfate free radicals released by the floating slow-release persulfate oxidizing material are in the same spatial position as the floating petroleum hydrocarbon pollutants, so as to provide on-site oxidation and remediation.

[0049] Specifically, in contaminated sites such as petrochemical plants or gas stations, lightweight non-aqueous liquids (such as gasoline, diesel, and other petroleum hydrocarbons) have a lower density than water and typically float on the surface of shallow groundwater, forming an oil film. Traditional oxidative remediation materials (such as cement-based and sand-based slow-release materials) have a high density and sink directly to the bottom of the water or are buried in the soil after being applied. This results in the oxidant being released at the bottom while the contaminants float on top, leading to extremely low remediation efficiency.

[0050] This embodiment utilizes the natural hydrophobicity and low density of the paraffin shell, allowing the material to float steadily on the water surface like a buoy. This means that the source of the oxidant (sulfate free radicals) is at the same vertical spatial height as the floating petroleum hydrocarbon pollutants. Persulfate can directly contact the pollutants upon exiting the pores, achieving true on-site, in-situ oxidative remediation, greatly improving the utilization rate of persulfate and the degradation rate of pollutants.

[0051] Furthermore, traditional methods of directly adding persulfate or simply mixing it with materials often result in rapid release within the first few days or weeks (i.e., explosive release), leading to persulfate waste and a potential rebound in pollutant concentration later on. This embodiment utilizes a triple slow-release mechanism—physical isolation through a paraffin shell, chemical inhibition through an HPMC gel network, and microporous flow restriction—to extend the persulfate release period to over 150 days. For in-situ groundwater remediation projects, this means a single application can maintain continuous remediation for approximately six months, eliminating the need for frequent persulfate replenishment and significantly reducing maintenance costs and labor input.

[0052] This embodiment provides an application of a floating, slow-release persulfate oxidizing material. Utilizing the natural hydrophobicity and low density of the paraffin shell, it can float steadily like a buoy on the surface of shallow groundwater accumulation areas or non-aqueous liquid contamination layers. This ensures that the release source of the oxidant (sulfate free radicals) is in the same vertical spatial position as the floating petroleum hydrocarbon pollutants, thus achieving true on-site, in-situ oxidation remediation. This significantly improves the utilization rate of persulfate and the degradation rate of pollutants, effectively solving the problem that traditional high-density oxidation remediation materials (such as cement-based and sand-based slow-release materials) sink to the bottom or are buried after deployment. In soil, this leads to the problem of oxidants being released at the bottom while contaminants float on top, resulting in extremely low remediation efficiency. Simultaneously, through a triple slow-release mechanism of physical isolation by the paraffin shell, chemical hindrance by the HPMC gel network, and microporous flow restriction, the release cycle of persulfate is extended. This allows for a single application to maintain continuous remediation for up to six months, eliminating the need for frequent persulfate replenishment. This not only avoids the waste of persulfate and the subsequent rebound of contaminant concentrations caused by the rapid release of persulfate within the initial days or weeks of traditional direct application or simple mixing of materials, but also significantly reduces engineering maintenance costs and labor input. In summary, this material offers multiple technical advantages in shallow groundwater accumulation areas or non-aqueous liquid contaminated layers, including precise targeting, efficient degradation, long-term slow release, and low operation and maintenance costs.

[0053] To better explain and facilitate understanding of this application, a detailed description of its specific embodiments is provided below. Unless otherwise specified in the embodiments, all raw materials used in the embodiments of this application are purchased commercially.

[0054] Example 1: Effect of different numbers of release pores on persulfate release performance Preparation of floating slow-release persulfate oxidizing materials: Step 1: Pour molten paraffin wax into a mold, let it cool and solidify, then demold to obtain a paraffin wax shell closed at one end; Step 2: Weigh out hydroxypropyl methylcellulose and persulfate according to the mass ratio, mix them evenly to obtain a mixed powder; Step 3: Compactly fill the inside of the paraffin shell with the mixed powder, and seal the other end with molten paraffin; Step 4: Using a heated needle, pierce both ends of the paraffin shell vertically to form release holes.

[0055] Keep the paraffin shell dimensions (3cm in diameter, 5cm in height, 3mm in wall thickness) and the core formulation (HPMC viscosity 100000mPa•s, HPMC:potassium persulfate mass ratio 1.5:1, filling degree 85%) consistent, only change the number of release holes on both ends.

[0056] Four groups of experimental samples were set up: Sample A: One release hole (0.3mm in diameter) is made on each of the two end faces; Sample B: Two release holes (0.3 mm in diameter) are made on each of the two end faces; Sample C: Three release holes (0.3 mm in diameter) are made on each of the two end faces; Sample D: Four release holes (0.3 mm in diameter) are made on each of the two end faces.

[0057] The above samples were placed in beakers containing 1L of deionized water to simulate a static aquatic environment. Persulfate concentrations in the water were measured at regular intervals, and release curves were plotted.

[0058] Experimental results are as follows Figure 5 As shown in the figure: (1) Controllability of release: The cumulative release concentration of persulfate in all four samples showed a good linear growth trend over time. This indicates that the material has stable release kinetics and does not exhibit the explosive release (burst release) phenomenon seen in traditional particulate oxidants in the initial stage of water immersion. This is attributed to the physical isolation effect of the paraffin shell and the effective inhibition of diffusion by the high-viscosity gel network formed after the HPMC core absorbs water.

[0059] (2) The effect of the number of pores: The number of release pores significantly affects the release rate.

[0060] When only one release well is set (sample A), the cumulative concentration at 30 days is low (approximately 160 mg / L) and the release rate is slow, making it suitable for long-term maintenance scenarios requiring extremely low concentrations. When two release wells were set (sample B), the cumulative concentration over 30 days increased to approximately 1000 mg / L, and the release flux increased significantly. When 3 (sample C) and 4 (sample D) release wells are set, the cumulative concentrations over 30 days reach approximately 1350 mg / L and 2200 mg / L or more, respectively.

[0061] Data shows that the persulfate release flux can be precisely controlled by adjusting the number of release holes. For general shallow groundwater petroleum hydrocarbon pollution remediation, in order to ensure the maintenance of an effective persulfate concentration in the water body (usually greater than 500-1000 mg / L) while also considering long-term effectiveness (>150 days), setting 2-4 release holes (i.e., a total of 4-8 holes, or 2-4 holes on one side) is a more ideal choice.

[0062] Example 2: Effect of different coating structures on the sustained-release performance of persulfate To verify the superiority of the paraffin shell + HPMC inner core dual sustained-release structure of this application, three sets of comparative experiments were set up in this embodiment to investigate the effects of single HPMC coating, single paraffin coating and the double-layer structure of this application on persulfate release behavior.

[0063] Comparative Example 1 (HPMC Single-Component Coating): Potassium persulfate and HPMC were mixed and compressed into tablets without an external paraffin shell, and placed directly in water. This simulated the case of chemical gel retardation alone.

[0064] Comparative Example 2 (Single-component paraffin coating): Pure potassium persulfate powder was filled into a paraffin shell, sealed, and perforated. No HPMC was added inside. This simulates the case of only physical isolation.

[0065] Example group (paraffin + HPMC double layer coating): prepared by the method of Example 1, that is, the paraffin shell is filled with a mixture of HPMC and persulfate powder.

[0066] The three groups of materials were placed into containers filled with deionized water, and samples were taken periodically to determine the concentration of persulfate in the water. The cumulative release percentage was calculated. The experimental results are as follows: Figure 6 As shown in the figure, the release kinetics of the three structures differ significantly: Comparative Example 1 (HPMC single-component coating) exhibited typical rapid release characteristics, with a cumulative release of over 80% within the first 15 days and complete release in approximately 30 days. This indicates that the gel network formed solely by HPMC, without external physical isolation, cannot effectively resist rapid water infiltration and rapid dissolution of persulfates, and thus cannot meet the long-term requirements for groundwater remediation.

[0067] Comparative Example 2 (paraffin single-component coating) although the paraffin shell isolated part of the water, more than 60% of potassium persulfate was still released in the first 15 days. This is because the lack of viscosity retardation from the internal HPMC gel allowed water entering the shell to rapidly dissolve the dry powdered potassium persulfate, resulting in rapid diffusion driven by a high concentration gradient (i.e., "burst release"), leading to a large waste of potassium persulfate in the early stages and insufficient remediation capacity in the later stages.

[0068] The example group (paraffin + HPMC double-layer coating) exhibited excellent sustained-release performance. During the first 60-day testing period, the cumulative release was only about 30%, and the release curve showed good linearity (zero-order release kinetics). Extrapolating from this linear trend (the purple dashed line in the figure), the complete release period of this material can be extended to over 150 days.

[0069] Therefore, the paraffin physical isolation + HPMC gel blocking synergistic mechanism adopted in this embodiment is not a simple functional superposition, but rather produces a significant synergistic effect. The paraffin shell transforms surface release into point release, while the HPMC gel transforms rapid diffusion into slow infiltration. It is this dual control mechanism that successfully solves the problem of excessively rapid release of traditional materials, achieving stable and long-term release for more than 150 days, which fully meets the actual engineering requirements for in-situ remediation of shallow groundwater.

[0070] Example 3: Effect of different mixing ratios of HPMC and persulfate on release performance The preparation method of Example 1 was used, maintaining the same paraffin shell structure, pore size, and filling degree, with only the core formulation changed. Specific groupings are shown in the table below: The floating slow-release materials prepared in each group were placed in a constant-temperature simulated groundwater environment, and the cumulative concentration of persulfate in the water was measured periodically every 127 days. The test results are as follows: Figure 7 As shown.

[0071] (1) Initial stability comparison (0~70 days): Verify the "anti-sudden release" capability.

[0072] As shown in the graph, during the first 70 days of the experiment: Experimental group A (1:1) and experimental group B (2:1): The concentration increased extremely slowly, remaining at a low level (<70 mg / L). This indicates that when the HPMC content is high, the formed gel network is dense and has high viscosity, which can effectively block the entry of water and the diffusion of persulfate, completely avoiding the "explosive release" phenomenon.

[0073] Experimental group C (1:2): The concentration increased sharply from day 10, reaching 367.45 mg / L on day 20, and soaring to 1601.58 mg / L on day 49. This indicates that when the ratio is too high (insufficient HPMC), the gel skeleton has weak support and cannot effectively control the initial release rate, which can easily lead to excessively high local concentrations, resulting in waste of persulfate or uncontrolled side reactions.

[0074] (2) Comparison of mid-to-late stage release characteristics (70~127 days): Verification of "long-lasting effect".

[0075] Experimental group C (1:2): Although the release was high in the early stage, the curve flattened out after 105 days (plateau phase), and the final concentration was approximately 6536 mg / L. This indicates that due to the rapid release in the early stage, the effective ingredients were depleted prematurely, resulting in insufficient repair momentum in the later stage, which could not meet the long-term repair needs.

[0076] Experimental group A (1:1): A steady, accelerated release trend emerged after 77 days. The concentration increased from 693.74 mg / L at day 77 to 5187.93 mg / L at day 127, an increase of approximately 7.5 times. More importantly, the concentration remained on an upward trend until the end of the experiment (127 days), without a significant plateau. This demonstrates that the 1:1 ratio ensured both initial safety and sufficient reserves of persulfate for long-term, continuous repair.

[0077] Experimental group B (2:1): Although the release was the most stable, the final cumulative concentration (approximately 3042 mg / L) was significantly lower than that of experimental group A. This indicates that while excessive HPMC may have a good sustained-release effect, the effective persulfate loading per unit volume is too low, which may lead to substandard remediation efficiency.

[0078] A comprehensive comparison shows that 1:1 (experimental group A) is the optimal ratio.

[0079] Compared to 1:2, it successfully solved the problems of early burst release and insufficient power in the later stage; Compared to 2:1, it significantly increases the total release of active ingredients and the duration of action while maintaining good sustained-release properties.

[0080] Therefore, in this embodiment, the preferred mass ratio of HPMC to persulfate is 1:1, which achieves the best balance between safety and efficiency.

[0081] Example 4: Effect of different viscosity grades of HPMC on the sustained-release performance of persulfate The preparation method of Example 1 was used, maintaining the same paraffin shell structure, pore size, filling degree, and HPMC to persulfate mass ratio (1:1), only changing the viscosity grade of HPMC. Specific groupings are shown in the table below: The two groups of floating slow-release materials prepared above were placed in a constant-temperature simulated groundwater environment, and the cumulative concentration of persulfate in the water was measured periodically, with a monitoring period of 127 days. The test results are as follows: Figure 8 As shown.

[0082] (1) Comparison of early burst release control capabilities (0-70 days) Experimental group A (Class II - 10w): exhibited excellent sustained-release properties. During the first 70 days, the concentration increased extremely slowly, with a cumulative concentration of only 61.85 mg / L at 70 days. This indicates that the high-viscosity HPMC formed a dense, high-strength gel network after absorbing water, greatly increasing the resistance to water molecule entry and ion diffusion, effectively preventing early drug loss.

[0083] Experimental group B (Class II-400): exhibited a significant burst release phenomenon. The concentration increased rapidly from day 6, reaching 184 mg / L on day 10, soaring to 640.56 mg / L on day 20, and reaching a high of 3767.56 mg / L by day 70. This indicates that the gel skeleton formed by low-viscosity HPMC is loose and cannot effectively block the diffusion of high-concentration drug solutions.

[0084] (2) Comparison of release duration and cycle (70~127 days) Experimental Group B (Class II-400): Although the release was rapid in the early stages, its potency was insufficient. The concentration reached its peak (approximately 5166 mg / L) around day 84, after which the curve flattened out and entered a plateau phase, with the concentration only slightly increasing to 5381.31 mg / L by day 127. This indicates that the persulfate in the low viscosity group was almost completely released in the early stages, making it unable to maintain long-term repair.

[0085] Experimental group A (Class II - 10w): demonstrated excellent long-acting release potential. Starting from day 77, the concentration jumped significantly (693.74 mg / L), and then maintained a continuous high-speed growth trend. By day 127, the concentration reached 5187.93 mg / L, and the curve slope remained steep, with no signs of a plateau.

[0086] The comparative results show that Type II-10w (high viscosity) is significantly superior to Type II-400 (low viscosity). Type II-10w successfully avoided the violent burst release in the first 70 days, preventing side reactions or environmental impacts caused by excessively high local concentrations. Type II-400 essentially became ineffective after 84 days, while Type II-10w remained in an active release phase at 127 days. If observation continues, its effective release period will far exceed 127 days, fully meeting the technical requirement of a sustained-release time greater than 150 days. Therefore, this application preferably uses the higher viscosity Type II-10w HPMC as the sustained-release matrix.

[0087] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0088] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

[0089] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A floating slow-release persulfate oxidizing material, characterized by, include: The paraffin shell has a cylindrical, closed structure to provide hydrophobic buoyancy and physical isolation; release holes are provided on both ends of the paraffin shell, which serve as channels for external water to enter. The inner core, which fills the interior of the paraffin shell, is composed of a dry powder matrix made of a mixture of hydroxypropyl methylcellulose and persulfate. The inner core forms a gel network after absorbing water, which is used to inhibit the dissolution and diffusion rate of persulfate.

2. The floating slow-release persulfate oxidation material according to claim 1, wherein, The viscosity of the hydroxypropyl methylcellulose is 80,000-120,000 mPa•s.

3. The floating slow-release persulfate oxidation material according to claim 1, characterized in that, The mass ratio of the hydroxypropyl methylcellulose to the persulfate is 1:1 to 2:

1.

4. The floating slow-release persulfate oxidation material according to claim 1, characterized in that, The persulfate is one of potassium persulfate, ammonium persulfate, or sodium persulfate.

5. The floating slow-release persulfate oxidizing material according to claim 1, characterized in that, The number of release holes on each end face is 2-5, and the diameter of each release hole is 0.2-0.5mm.

6. The floating slow-release persulfate oxidizing material according to claim 1, characterized in that, The particle size of the dry powder matrix is ​​less than or equal to 100 mesh.

7. A method for preparing a floating slow-release persulfate oxidizing material, characterized in that, The preparation method includes: Molten paraffin wax is poured into a mold, cooled and solidified, and then demolded to obtain a paraffin wax shell closed at one end. Weigh out hydroxypropyl methylcellulose and persulfate according to the mass ratio, mix them evenly to obtain a mixed powder; The mixed powder is compacted into the interior of the paraffin shell, and the other end is sealed with molten paraffin. Using a heated needle, vertically puncture both ends of the paraffin shell to form release holes.

8. The preparation method according to claim 7, characterized in that, The compact filler has a fill rate of 80% or higher.

9. An application of a floating slow-release persulfate oxidizing material, characterized in that, The floating slow-release persulfate oxidizing material according to any one of claims 1-6 or the floating slow-release persulfate oxidizing material prepared by the preparation method according to any one of claims 7-8 is applied to shallow groundwater accumulation areas or non-aqueous liquid contamination layers; The floating slow-release persulfate oxidizing material utilizes the hydrophobicity of the paraffin shell to float on the surface of the water, so that the sulfate free radicals released by the floating slow-release persulfate oxidizing material are in the same spatial position as the floating petroleum hydrocarbon pollutants, so as to provide on-site oxidation and remediation.

10. The application according to claim 9, characterized in that, The release time of the floating slow-release persulfate oxidant material is greater than 150 days.

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