Sustained-release material, permeable reactive barrier and underground water remediation system

Abstract

The invention relates to a sustained-release material, a permeable reactive barrier and an underground water remediation system.The sustained-release material comprises a core material and a matrix, and the core material is embedded in the matrix; the core material is selected from one of an acidic material and an alkaline material, and the matrix is selected from one or more of a polymer material and a wax material. According to the method, the pH value required by the optimal reaction in the PRB reaction zone can be regulated and controlled, and the pH value of the treated underground water can be maintained in a neutral range of an environmental standard.

Description

A slow-release material, a permeable reactive wall, and a groundwater remediation system Technical Field

[0001] This disclosure relates to the fields of environmental engineering and groundwater remediation, specifically to a slow-release material, a permeable reactive wall, and a groundwater remediation system. Background Technology

[0002] Permeable reactive barriers (PRBs) are a widely used environmental remediation technology for groundwater treatment. They utilize a layer of reactive material placed along the flow path of contaminated groundwater to remove or transform dissolved contaminants through chemical, biological, or physical processes. The advantage of this technology is its ability to continuously and effectively treat flowing groundwater with minimal surface disturbance.

[0003] pH is a key factor affecting reaction efficiency during PRB operation. For example, when using zero-valent iron (ZVI) to treat nitrate or hexavalent chromium (Cr(VI)) pollution, acidic conditions significantly improve the reaction rate and removal rate. However, under neutral or alkaline conditions, the treatment rate and pollutant removal rate decrease significantly, which is particularly detrimental to high-load pollution treatment. Furthermore, over time, the large amount of iron oxides generated during the reaction can cause aggregation, a common phenomenon that can lead to PRB blockage in severe cases, thus reducing its lifespan. The current conventional solution is to periodically inject acid to dissolve the iron oxides, but this method is cumbersome, costly, and the pH of the water is often acidic after each injection, resulting in treated water with a pH that often fails to meet standards.

[0004] When treating certain organic pollutants, such as using slow-release persulfate methylene blue, alkaline conditions can activate persulfate, effectively increasing the decomposition rate and degradation efficiency. However, the resulting water has a slightly alkaline pH, which limits the widespread application of PRB. Therefore, regulating the pH of the treated water to maintain it at neutral is crucial for improving the application of PRB. Summary of the Invention

[0005] The purpose of this disclosure is to provide a slow-release material, a permeable reactive barrier, and a groundwater remediation system that can regulate the optimal pH value required for the reaction within the PRB reaction zone and ensure that the pH value of the treated groundwater can be maintained within the neutral range of environmental standards.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a sustained-release material, comprising a core material and a matrix, wherein the core material is embedded in the matrix; the core material is selected from one of acidic materials and alkaline materials, and the matrix is ​​selected from one or more of polymeric materials and waxy materials.

[0007] Optionally, the core material is an acidic material, and the slow-release material releases H... + The release rate is 0.1~10 mg / (g·d), preferably 1~5 mg / (g·d); or, the core material is an alkaline material, and the sustained-release material releases OH... - The rate is 0.2~20 mg / (g·d), preferably 1~5 mg / (g·d).

[0008] Optionally, the content of the core material is 1 to 50% by weight, preferably 10 to 30% by weight, based on the total weight of the sustained-release material.

[0009] Optionally, the polymer material is selected from one or more of synthetic polymers and natural polymers; preferably, the synthetic polymer is selected from one or more of polystyrene, acrylonitrile-styrene-butadiene copolymer, polyvinyl chloride, polyacrylonitrile, and acrylonitrile-butadiene copolymer; the natural polymer is selected from one or more of sodium alginate, starch, and gelatin; optionally, the wax material is selected from one or more of paraffin wax, stearic acid, and sodium stearate.

[0010] Optionally, the acidic material is selected from one or more of oxalic acid, citric acid, sodium bisulfate, sodium bisulfite, and calcium dihydrogen phosphate; alternatively, the alkaline material is selected from one or more of sodium carbonate, sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium acetate.

[0011] A second aspect of this disclosure provides a permeable reactive wall, wherein along the material flow direction in the permeable reactive wall, the permeable reactive wall includes an active reaction zone and a pH balance zone connected in sequence; the active reaction zone includes a first slow-release material, and the pH balance zone includes a second slow-release material; the first slow-release material and the second slow-release material each independently include the slow-release material described in the first aspect of this disclosure, and the core materials of the first slow-release material and the second slow-release material have different acidity and alkalinity.

[0012] Optionally, the pH value of the active reaction zone is 2 to 11; preferably, the active reaction zone is acidic and the core material of the first sustained-release material is acidic; the active reaction zone is alkaline and the core material of the first sustained-release material is alkaline.

[0013] Optionally, the active reaction zone further includes a first filling material; the first filling material is selected from an acidic active reaction medium or an alkaline active reaction medium; optionally, based on the total weight of the first sustained-release material and the active reaction medium, the content of the first sustained-release material is 1 to 10% by weight, preferably 2 to 6% by weight.

[0014] Optionally, the pH balance zone includes a second filling material; the second filling material includes a supportive and non-reactive framework material, and the second filling material is selected from one or more of sand, gravel and ceramsite; preferably, based on the total amount of the second filling material in the pH balance zone, the content of the second slow-release material in the pH balance zone is 0.1 to 10% by weight, preferably 1 to 2% by weight.

[0015] This disclosure provides a groundwater remediation system in a third aspect, including a monitoring unit and the permeable reactive barrier described in the second aspect of this disclosure; the monitoring unit is used to monitor the pH value in the active reaction zone and the pH balance zone in real time.

[0016] Through the above technical solutions, this disclosure provides a slow-release material, a permeable reactive barrier, and a groundwater remediation system. The core material (acidic or alkaline material) of the slow-release material is embedded in the matrix, so that the active substances of the core material can be released slowly and continuously over a long period of time. Setting the slow-release material in the active reaction zone and pH balance zone of the permeable reactive barrier has at least the following beneficial effects: (1) Optimal pH control: Based on the actual pollution situation and chemical requirements of the groundwater, the optimal pH value of the reaction section can be maintained for a long time to optimize the reaction conditions; (2) Reduced maintenance requirements: Reduced frequent maintenance and chemical injection required due to pH runaway, reducing operational complexity and long-term costs; (3) Improved system lifespan: Extended effective operating time of the PRB system by preventing excessive aggregation and blockage of iron oxides; (4) Effective control and adjustment of the chemical reaction environment in the PRB system, making it more adaptable to complex pollution conditions, improving treatment efficiency and environmental safety; (5) Also ensures that the pH value of the treated groundwater can be maintained within the neutral range of environmental standards.

[0017] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 is a comparative experimental diagram of the removal effect of Cr(VI) by a permeable reactive wall simulated column based on a controlled pH of a slow-release material in Embodiments 1, 3, 4 and Comparative Example 1; Figure 2 is a comparative experimental diagram of the removal effect of methylene blue by a permeable reactive wall simulated column based on a controlled pH of a slow-release material in Embodiments 2 and Comparative Example 2; Figure 3 is a comparative experimental diagram of the removal effect of Cr(VI) by a permeable reactive wall simulated column based on a controlled pH of a slow-release material in Embodiments 5-8 of the present disclosure. Detailed Implementation

[0019] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; 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.

[0020] The first aspect of this disclosure provides a sustained-release material, comprising a core material and a matrix, wherein the core material is embedded in the matrix; the core material is selected from one of acidic materials and alkaline materials, and the matrix is ​​selected from one or more of polymeric materials and waxy materials.

[0021] This disclosure provides a slow-release material in which the core material (acidic or alkaline material) is embedded in a matrix, enabling the active substances in the core material to be released slowly and continuously over a longer period of time, providing an innovative technical approach for the effective treatment of complex groundwater pollution.

[0022] In one embodiment, the core material is an acidic material, and the slow-release material releases H... + The release rate is 0.1~10 mg / (g·d), preferably 1~5 mg / (g·d); or, the core material is an alkaline material, and the sustained-release material releases OH... - The rate of H release is 0.2–20 mg / (g·d), preferably 1–5 mg / (g·d). + Rate and release of OH - The rate was calculated after testing with a high-precision pH meter in a typical groundwater environment. "mg / (g·d)" represents the H₂ released per unit mass of slow-release material per day. + or OH - The quality. It has the H released in this embodiment. + Rate and release of OH - The rate-controlled release material can meet the needs of different chemical reactions, achieve better pH control in the PRB system, and maintain the long-term operation of the PRB system.

[0023] In one embodiment, the core material content is 1-50% by weight, preferably 10-30% by weight, based on the total weight of the sustained-release material. When the core material content in the sustained-release material is within the range of this embodiment, especially within the preferred range, the sustained-release material can have better sustained-release performance, thereby further improving its pH precision control effect in the active reaction zone.

[0024] In one specific embodiment, the polymer material is selected from one or more synthetic polymers and natural polymers; preferably, the synthetic polymer is selected from one or more polystyrene, acrylonitrile-styrene-butadiene copolymer, polyvinyl chloride, polyacrylonitrile, and acrylonitrile-butadiene copolymer; the natural polymer is selected from one or more sodium alginate, starch, and gelatin; and the wax material is selected from one or more paraffin wax, stearic acid, and sodium stearate. Both the polymer material and the wax material provided in this embodiment can achieve excellent coating effects on the core material and enable the slow-release material to have an excellent ion release rate.

[0025] In one embodiment, the acidic material is selected from one or more of oxalic acid, citric acid, sodium bisulfate, sodium bisulfite, and calcium dihydrogen phosphate; optionally, the alkaline material is selected from one or more of sodium carbonate, sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium acetate. Using the acidic or alkaline materials provided in this disclosure allows for the control of the optimal reaction pH value within the PRB reaction zone.

[0026] In a preferred embodiment, the preparation method of the sustained-release material includes the following steps: (1) thoroughly mixing the core material components with the matrix, and converting the matrix into a liquid state by heating or adding solvents, so that the core material particles are surrounded by the liquid matrix; (2) dividing the mixture in (1) into plastic parts by means of molds or cutting, according to the usage requirements; (3) solidifying the liquid matrix to form sustained-release material particles by adjusting experimental conditions such as cooling or solvent removal. The specific process conditions can be adjusted according to the reagent requirements.

[0027] A second aspect of this disclosure provides a permeable reactive wall, wherein along the material flow direction in the permeable reactive wall, the permeable reactive wall includes an active reaction zone and a pH balance zone connected in sequence; the active reaction zone includes a first slow-release material, and the pH balance zone includes a second slow-release material; the first slow-release material and the second slow-release material each independently include the slow-release material described in the first aspect of this disclosure, and the core materials of the first slow-release material and the second slow-release material have different acidity and alkalinity.

[0028] This disclosure provides a permeable reactive barrier that ensures contaminated groundwater first flows through an active reaction zone for necessary chemical treatment, and then through a pH equilibration zone for final adjustment, to avoid material mixing between the two zones while allowing water to flow freely. The slow-release material is placed in the active reaction zone and the pH equilibration zone of the permeable reactive barrier, which has at least the following beneficial effects: (1) Optimal pH control: Based on the actual pollution and chemical requirements of the groundwater, the optimal pH value of the reaction section can be maintained for a long time to optimize the reaction conditions; (2) Reduced maintenance requirements: Reduced frequent maintenance and chemical injection required due to pH runaway, reducing operational complexity and long-term costs; (3) Increased system lifespan: Extended effective operating time of the PRB system by preventing excessive aggregation and blockage of iron oxides; (4) Effective control and adjustment of the chemical reaction environment in the PRB system, making it more adaptable to complex pollution conditions, improving treatment efficiency and environmental safety; (5) It also ensures that the pH value of the treated groundwater can be maintained within the neutral range of environmental standards.

[0029] In the permeable reactive barrier provided in this disclosure, the acidic and alkaline materials of the core material of the first slow-release material in the active reaction zone can be selected according to the type and concentration of the wastewater to be treated, in order to optimize reaction efficiency and final water quality. In this disclosure, the acidity or alkalinity of the core material of the second slow-release material in the pH balance zone is opposite to that of the core material of the first slow-release material, to ensure efficient pH balance.

[0030] In one embodiment, the pH value of the active reaction zone is 2 to 11; in this disclosure, the pH value can be adjusted to the optimal reaction range according to the chemical treatment requirements of pollutants.

[0031] In one specific embodiment, the active reaction zone is acidic, and the core material of the first sustained-release material is an acidic material; or the active reaction zone is alkaline, and the core material of the first sustained-release material is an alkaline material.

[0032] In one embodiment, the active reaction zone further includes a first filling material; the first filling material is selected from an acidic active reaction medium or an alkaline active reaction medium; in this disclosure, the active reaction zone is selected from conventional acidic or alkaline active reaction medium materials in the art, depending on the target pollutant, to achieve excellent neutralization effect.

[0033] In a preferred embodiment, based on the total weight of the first sustained-release material and the active reaction medium material, the content of the first sustained-release material is 1-10% by weight, preferably 2-6% by weight. The content of the first sustained-release material in this disclosure can be determined according to the nature of the pollutant and the required pH environment.

[0034] In one specific embodiment, the acidic active reaction medium material in the filling material of the active reaction zone includes, but is not limited to, iron powder (zero-valent iron), Fe / N bimetallic materials, etc.; the alkaline active reaction medium material includes, but is not limited to, sodium persulfate, ferrate, etc. After the first sustained-release material provided in this disclosure is released, it can activate the active reaction medium in the active reaction zone to improve the treatment effect. The filling material can be used in conjunction with filling additives, including but not limited to sand, gravel, and ceramsite. The alkaline active reaction medium can also be prepared as a sustained-release material, and its preparation method is similar to that of the aforementioned sustained-release material preparation method, and will not be repeated here.

[0035] In one embodiment, the pH balance zone includes a second filler material; the second filler material includes a supportive and non-reactive skeletal material such as sand, gravel, and ceramsite; preferably, based on the total amount of the second filler material in the pH balance zone, the content of the second slow-release material in the pH balance zone is 0.1-10% by weight, more preferably 1-2% by weight. The second slow-release material is set in the pH balance zone according to the content in this embodiment, and the properties of the second slow-release material are opposite to the acidity / alkalinity of the first slow-release material to ensure effective pH balance.

[0036] In one specific embodiment, the target pH range of the pH balance zone is 6.5 to 8.5.

[0037] This disclosure provides a groundwater remediation system, including a monitoring unit and the permeable reactive barrier described in the second aspect of this disclosure; the monitoring unit is used to monitor the pH value in the active reaction zone and the pH balance zone in real time, and can evaluate the remediation effect of the permeable reactive barrier and determine the timing of filling material replacement to maintain the effectiveness of groundwater remediation.

[0038] In this disclosure, the monitoring unit can be a device conventional in the art.

[0039] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0040] The following preparation examples illustrate the preparation method of sustained-release materials (sustainable-release acid materials or sustained-release alkali materials).

[0041] Preparation Example 1 This preparation example illustrates the preparation method of a slow-release acid material (paraffin-embedded sodium bisulfate), comprising the following steps: 90 parts by weight of 56# paraffin wax is heated to 60°C and melted. Then, 10 parts by weight of sodium bisulfate powder is added and stirred thoroughly to ensure uniform dispersion in the liquid paraffin. The suspension is then poured into a silicone mold with a single cell diameter of 20 mm and cooled to form a slow-release acid material with a particle size of 20 mm and a sodium bisulfate content of 10% by weight.

[0042] Preparation Example 2: This preparation example illustrates the preparation method of a slow-release alkali material (paraffin-embedded sodium carbonate), comprising the following steps: 85 parts by weight of 56# paraffin wax is heated to 60°C and melted; then 15 parts by weight of sodium carbonate powder is added and stirred thoroughly to ensure uniform dispersion in the liquid paraffin. The suspension is then poured into a silicone mold with a single cell diameter of 20 mm and cooled to form a slow-release alkali material with a particle size of 20 mm and a sodium carbonate content of 15% by weight.

[0043] Preparation Example 3: This preparation example illustrates the preparation method of a slow-release alkali material (waste polystyrene foam encapsulated with sodium hydroxide), comprising the following steps: 10 parts by weight of dichloromethane solvent are used to dissolve 90 parts by weight of waste polystyrene foam to obtain a viscous polystyrene solution. Then, 15 g of sodium hydroxide powder is weighed and added to the above solution and stirred thoroughly to obtain a dough-like core material and a substrate mixture. The dough-like mixture is cut and granulated using a pelletizing machine, and after drying at 35°C, a slow-release alkali material with a particle size of 6 mm and a sodium hydroxide content of 10% by weight is obtained.

[0044] Preparation Example 4: This preparation example illustrates the preparation method of a slow-release acid material (paraffin-embedded oxalic acid), comprising the following steps: 90 parts by weight of 56# paraffin wax is heated to 60°C and melted; then 10 parts by weight of oxalic acid powder is added and stirred thoroughly to ensure uniform dispersion in the liquid paraffin. The suspension is then poured into a silicone mold with a single cell diameter of 20 mm and cooled to form a slow-release acid material with a particle size of 20 mm and an oxalic acid content of 10% by weight.

[0045] Preparation Example 5 This preparation example is based on the method in Preparation Example 1, except that the mass fraction of the matrix paraffin is 40, the mass fraction of the core material sodium bisulfate is 60, and the core material content in the prepared slow-release acid material is 60 by weight.

[0046] Preparation Example 6 This preparation example follows the method in Preparation Example 1, except that the mass part of the matrix paraffin is 83, the mass part of the core material sodium bisulfate is 17, and the core material content in the prepared slow-release acid material is 17% by weight.

[0047] Preparation Example 7: This preparation example follows the method in Preparation Example 2, but differs from Preparation Example 1 in that: 77 parts by weight of 56# paraffin and 23 parts by weight of sodium carbonate powder are used to prepare a slow-release alkali material with a particle size of 20 mm and a sodium carbonate content of 23% by weight.

[0048] The release rate of the sustained-release material obtained in the above preparation example was tested using the following method: 1 g of sustained-release material was added to 1000 mL of distilled water at 25 °C. The pH of the solution was measured at 0, 24, 48, 72, 96, and 120 h using a high-precision pH meter. The cumulative internal H2 released by the sustained-release acid material within the release time period t was calculated using the following formula (1). + mass m ac Establish m ac -t standard curve to obtain H of slow-release alkali material + Release rate; the cumulative OH- released by the slow-release alkali material within the release time period t is calculated using the following formula (2). - mass m al Establish m al The OH- of the slow-release alkaline material was obtained from the standard curve. - Release rate.

[0049] m ac= 10 -pH ×V (1); where V is the solution volume, L; m al= 10 pH-14 ×V×17 (2); where V is the solution volume, L.

[0050] The properties of the sustained-release materials obtained from the above preparation examples are listed in Table 1 below.

[0051] Table 1

[0052] The following examples illustrate the application of the slow-release materials and permeable reactive materials provided in this disclosure in groundwater remediation.

[0053] Example 1 This example provides a column experiment for removing hexavalent chromium (Cr(VI)) from water using zero-valent iron powder. The experiment utilizes laboratory simulation to verify a permeable reactive wall technology based on a slow-release material with controllable pH. The column in the permeable reactive wall has a diameter of 5 cm and a height of 20 cm, and consists of two zones: an active reaction zone and a pH equilibrium zone.

[0054] In the active reaction zone, the first filling material has a filling height of 8 cm. The first filling material is a mixture of iron powder (an acidic active reaction medium) and sand (a filling agent), with a mass ratio of iron powder to sand of 1:3. 1 g of paraffin-embedded sodium bisulfate is added to this zone as a slow-release acid material (the first slow-release material). Based on the total weight of the materials in the active reaction zone, the content of paraffin-embedded sodium bisulfate (the first slow-release material) is 2% by weight. Based on the total weight of the first slow-release material and the active reaction medium, the content of sodium bisulfate is 10% by weight, releasing H... +The average rate was 0.71 mg / (g·d), which maintained the pH in the active reaction zone between 3.4 and 4.1.

[0055] In the pH equilibrium zone, the filling height is 6 mm, and 1 g of paraffin-embedded sodium carbonate is used as a slow-release alkali material (second slow-release material). The pH equilibrium zone also includes medium sand, with the slow-release alkali material and medium sand serving as the second filling material. Based on the total amount of the slow-release alkali material and medium sand (second filling material) in the pH equilibrium zone, the content of the second slow-release material in the pH equilibrium zone is 1% by weight. Based on the total weight of the second slow-release material, the loading of sodium carbonate is 15% by weight, with an average OH release rate of [missing information]. - The rate was 0.94 mg / (g·d) to adjust the pH of the effluent to neutral (6.4~7.6).

[0056] The column experiment in this embodiment was conducted under the conditions of a water injection rate of 0.5 mL / min and an initial Cr(VI) concentration of 2.5 mg / L. After 20 days of operation, the Cr(VI) concentration was consistently below 0.05 mg / L, demonstrating the system's continuous and efficient removal capability of Cr(VI). The effluent pH was between 6.4 and 7.6, ensuring that the pH of the treated water remained within the neutral range.

[0057] Comparative Example 1: This comparative example refers to the apparatus and method in Example 1, except that slow-release acid and alkali materials were not used in the active reaction zone and pH equilibrium zone, while other conditions were the same as in Example 1.

[0058] The system in this comparative example without pH adjustment showed that the water pH value was between 7.3 and 8.1. The Cr(VI) removal effect curves in Example 1 and Comparative Example 1 are shown in Figure 1. It can be seen that, in the later stage of the experiment, the Cr(VI) concentration in this comparative example rebounded, indicating the importance of pH balance for maintaining long-term removal efficiency.

[0059] Comparing Example 1 with Comparative Example 1, it can be seen that by combining the active reaction zone and the pH balance zone, the permeable reactive wall provided by this disclosure not only effectively removes Cr(VI) but also ensures the stability of the effluent pH, demonstrating the application potential and environmental adaptability of this system in groundwater remediation.

[0060] Example 2 This example provides a column experiment to simulate the application of a slow-release material-based permeable reactive barrier technology for the removal of methylene blue from water. The experimental column is 5 cm in diameter and 20 cm high, and is divided into an active reaction zone and a pH equilibrium zone.

[0061] In the active reaction zone, the first filling material has a filling height of 8 cm. This first filling material comprises a mixture (mass ratio of 5:1) of slow-release sodium persulfate (an alkaline active reaction medium) and sand (a filling agent) to promote the chemical reaction of methylene blue. Additionally, 1 g of waste polystyrene foam-embedded sodium hydroxide is used as a slow-release alkaline material (the first slow-release material). Based on the total weight of the materials in the active reaction zone, the content of waste polystyrene foam-embedded sodium hydroxide (the first slow-release material) is 4% by weight. Based on the total weight of the first slow-release material and the active reaction medium, the content of sodium hydroxide is 10% by weight, releasing OH... - The reaction rate was 1.3 mg / (g·d), effectively maintaining the pH of the reaction zone between 10.4 and 11.3. The slow-release sodium persulfate material was prepared by the following method: 85 parts by weight of 56# paraffin wax was heated to 60°C and melted, then 15 parts by weight of sodium persulfate powder was added and stirred thoroughly to ensure uniform dispersion in the liquid paraffin wax. The suspension was then poured into a 20 mm diameter silicone mold and cooled to form a sodium persulfate material with a particle size of 20 mm and a sodium persulfate content of 15% by weight.

[0062] In the pH equilibrium zone, with a filling height of 8 mm, 1 g of paraffin-embedded oxalic acid was used as the slow-release acid material (second slow-release material). The pH equilibrium zone also included medium sand. Based on the total amount of the slow-release acid material and medium sand in the pH equilibrium zone, the content of the second slow-release material in the pH equilibrium zone was 0.8% by weight. Based on the total weight of the second slow-release material, the oxalic acid loading was 10% by weight, and the released H₂... + The rate was 0.81 mg / (g·d) to adjust the pH of the effluent to neutral (6.7~7.6).

[0063] Under the conditions of a water injection rate of 0.5 mL / min and an initial methylene blue concentration of 15 mg / L, the 20-day experiment showed that the methylene blue concentration was below 2 mg / L, proving that the system provided in this disclosure can efficiently remove methylene blue during continuous operation, and the pH value of the treated water is in the neutral range of 6.7 to 7.6.

[0064] Comparative Example 2: This comparative example refers to the apparatus and method in Example 2, except that no sustained-release material was used in the active reaction zone and pH equilibrium zone, while the other conditions were the same as in Example 2.

[0065] Figure 2 shows the methylene blue removal effect curves in Example 2 and Comparative Example 2. It can be seen that the removal of methylene blue was relatively good in the early stage of the experiment, and the pH value of the effluent was between 7.6 and 8.3. However, since the persulfate was not activated by the first slow-release material, the removal effect of methylene blue was still significantly lower than that of the simulated slow-release alkali column experiment in Example 2 during the entire column experiment. This reflects the possible decrease in treatment effect due to the lack of pH adjustment.

[0066] By integrating the strongly alkaline environment of the active reaction zone and the acidic adjustment of the pH balance zone, the permeable reactive wall provided in this disclosure not only ensures the effective removal of methylene blue by activating persulfate in an alkaline environment, but also maintains the stability of the effluent pH, demonstrating the application potential and environmental adaptability of this slow-release material technology in the treatment of organic pollutants such as methylene blue.

[0067] Example 3: This example refers to the apparatus and method in Example 1, except that the first sustained-release material in the active reaction zone is replaced with the paraffin-embedded sodium bisulfate obtained in Preparation Example 5, which releases H... + The average rate was 21.83 mg / (g·d), which maintained the pH in the active reaction zone between 1.7 and 2.5; the rest of the process was the same as in Example 1.

[0068] In this embodiment, after 20 days of experimental operation, the concentration of Cr(VI) was consistently below 0.05 mg / L, demonstrating the system's continuous and efficient removal capacity of Cr(VI). However, the effluent pH was acidic (between 2.7 and 5.4), failing to meet the remediation standards. Comparing this embodiment with Example 1 shows that the first slow-release material with an optimized acid release rate used in Example 1 achieves better results.

[0069] Example 4: This example follows the method described in Example 1, but differs in that the active reaction zone is filled to a height of 8 cm and uses a mixture of iron powder and sand in a mass ratio of 1:3. 8 g of paraffin-embedded sodium bisulfate is added to this zone as a slow-release acid material (first slow-release material). Based on the total weight of the first slow-release material and the active reaction medium in the active reaction zone, the content of paraffin-embedded sodium bisulfate (first slow-release material) is 16% by weight; the remaining processes are the same as in Example 1.

[0070] In this embodiment, the concentration of Cr(VI) was below 0.05 mg / L for the first 5 days of the experiment, demonstrating the system's continuous and efficient removal capacity of Cr(VI). However, the pH of the effluent was acidic (between 4.36 and 5.8). This indicates that adding the first slow-release material according to the optimized content provided in this disclosure in Example 1 can achieve a better treatment effect.

[0071] Example 5: This example refers to the apparatus and method in Example 1, except that the first sustained-release material in the active reaction zone is replaced with the paraffin-embedded sodium bisulfate obtained in Preparation Example 6, which releases H... + The average rate was 1.5 mg / (g·d), which maintained the pH in the active reaction zone between 3.1 and 3.7; the rest of the process was the same as in Example 1.

[0072] In this embodiment, after 20 days of experimental operation, the concentration of Cr(VI) was consistently below 0.05 mg / L, and the detected concentration was lower than that in Example 1, demonstrating the system's continuous and efficient removal capability of Cr(VI). The effluent pH value was between 6.3 and 7.4, ensuring that the pH value of the treated water was within the neutral range. Compared with Example 1, this embodiment demonstrates the use of a preferred H2 release... + The first sustained-release material with an average rate of release has better treatment effect.

[0073] Example 6: This example follows the method in Example 1, but differs in that the filling height of the active reaction zone is 8 cm, and a mixture of iron powder and sand is used, with a mass ratio of iron powder to sand of 1:3. 0.5 g of paraffin-embedded sodium bisulfate is added to this zone as a slow-release acid material (first slow-release material). Based on the total weight of the first slow-release material and the active reaction medium in the active reaction zone, the content of paraffin-embedded sodium bisulfate (first slow-release material) is 1% by weight; the remaining process is the same as in Example 1.

[0074] In this embodiment, after 20 days of experimental operation, the Cr(VI) concentration was consistently below 0.05 mg / L. However, the Cr(VI) concentration showed a slight upward trend in the later stages. Although the removal effect of this embodiment on Cr(VI) was slightly inferior to that of Example 1, it still demonstrated the system's continuous and efficient removal capability for Cr(VI). The pH value of the effluent from this system was between 6.4 and 7.4, ensuring that the pH value of the treated water was within the neutral range, thus avoiding the problem in Example 4 where the effluent pH did not meet the remediation standard. Comparing this embodiment with Example 4, it can be seen that this embodiment, with the addition amount of the first slow-release material provided in this disclosure, has a better treatment effect.

[0075] Example 7 This example follows the method in Example 1, except that the slow-release alkaline material in the pH equilibrium zone is replaced with the slow-release alkaline material (OH-) from Example 7. - The rate was 1.5 mg / (g·d); the rest of the process was the same as in Example 1.

[0076] In this embodiment, after 20 days of experimental operation, the concentration of Cr(VI) was consistently below 0.05 mg / L, and the removal effect was essentially the same as in Example 1, demonstrating the system's continuous and efficient removal capability of Cr(VI). The pH value of the effluent was between 6.6 and 7.6, ensuring that the pH value of the treated water remained stable near the neutral range. This indicates that the use of a second slow-release material with an optimized alkali release rate in this embodiment can achieve better results.

[0077] Example 8 This example refers to the method in Example 1, but differs from Example 1 in that: in the pH equilibrium zone, based on the total amount of the slow-release alkali material and the medium sand (second filling material) in the pH equilibrium zone, the content of the second slow-release material in the pH equilibrium zone is 10% by weight, and the rest of the process is the same as in Example 1.

[0078] In this embodiment, after 20 days of experimental operation, the concentration of Cr(VI) was consistently below 0.05 mg / L, and the removal effect was basically consistent with that of the previous embodiment, demonstrating the system's continuous and efficient removal capability of Cr(VI). However, the pH value of the effluent was between 7.2 and 8.1, indicating that the pH value of the treated water was slightly alkaline. Comparing this embodiment with Example 1 shows that adding the second slow-release material at the preferred content provided in this disclosure in Example 1 is necessary to obtain a better treatment effect.

[0079] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0080] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0081] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A sustained-release material, characterized in that, It includes a core material and a matrix, wherein the core material is embedded in the matrix; the core material is selected from one of acidic materials and alkaline materials, and the matrix is ​​selected from one or more of polymeric materials and waxy materials.

2. The sustained-release material according to claim 1, characterized in that, The core material is an acidic material, and the slow-release material releases H... + The release rate is 0.1~10 mg / (g·d), preferably 1~5 mg / (g·d); or, the core material is an alkaline material, and the sustained-release material releases OH... - The rate is 0.2~20 mg / (g·d), preferably 1~5 mg / (g·d).

3. The sustained-release material according to claim 1, characterized in that, Based on the total weight of the sustained-release material, the content of the core material is 1 to 50% by weight, preferably 10 to 30% by weight.

4. The sustained-release material according to claim 1, characterized in that, The polymer material is selected from one or more of synthetic polymers and natural polymers; preferably, the synthetic polymer is selected from one or more of polystyrene, acrylonitrile-styrene-butadiene copolymer, polyvinyl chloride, polyacrylonitrile, and acrylonitrile-butadiene copolymer; the natural polymer is selected from one or more of sodium alginate, starch, and gelatin; optionally, the wax material is selected from one or more of paraffin wax, stearic acid, and sodium stearate.

5. The sustained-release material according to claim 1, characterized in that, The acidic material is selected from one or more of oxalic acid, citric acid, sodium bisulfate, sodium bisulfite, and calcium dihydrogen phosphate; optionally, the alkaline material is selected from one or more of sodium carbonate, sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium acetate.

6. A permeable reactive wall, characterized in that, Along the material flow direction in the permeable reactive wall, the permeable reactive wall includes an active reaction zone and a pH balance zone connected in sequence; the active reaction zone includes a first sustained-release material, and the pH balance zone includes a second sustained-release material; the first sustained-release material and the second sustained-release material each independently include the sustained-release material according to any one of claims 1 to 5, and the core materials of the first sustained-release material and the second sustained-release material have different acidity and alkalinity.

7. The permeable reactive wall according to claim 6, characterized in that, The pH value of the active reaction zone is 2~11; preferably, the active reaction zone is acidic and the core material of the first sustained-release material is acidic; the active reaction zone is alkaline and the core material of the first sustained-release material is alkaline.

8. The permeable reactive wall according to claim 7, characterized in that, The active reaction zone further includes a first filling material; the first filling material is selected from an acidic active reaction medium or an alkaline active reaction medium; optionally, based on the total weight of the first sustained-release material and the active reaction medium, the content of the first sustained-release material is 1 to 10% by weight, preferably 2 to 6% by weight.

9. The permeable reactive wall according to claim 6, characterized in that, The pH balance zone includes a second filling material; the second filling material includes a supportive and non-reactive skeleton material, optionally selected from one or more of sand, gravel and ceramsite; preferably, based on the total amount of the second filling material in the pH balance zone, the content of the second slow-release material in the pH balance zone is 0.1 to 10% by weight, preferably 1 to 2% by weight.

10. A groundwater remediation system, characterized in that, It includes a monitoring unit and a permeable reactive wall as described in any one of claims 6 to 9; the monitoring unit is used to monitor the pH value in the active reaction zone and the pH balance zone in real time.

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