Preparation method of sustained-release material, prepared sustained-release material and application of sustained-release material

Abstract

The invention discloses a preparation method of a sustained-release material, the prepared sustained-release material and application of the sustained-release material. The method comprises the following steps: (1) dispersing first starch in water, then adding a first active substance, activated carbon and sodium alginate, and uniformly mixing to obtain a product I; (2) dispersing second starch in water, then adding a second active substance, and uniformly mixing to obtain a product II; and (3) mixing the product I obtained in the step (1), the product II obtained in the step (2), a strength agent, a matrix and a solvent, molding, and drying to obtain the sustained-release material. Wherein the first starch in the step (1) and / or the first starch in the step (2) is modified porous starch. The slow-release material prepared by the method has the characteristics of environmental friendliness and long-term release, can be used in the aspect of slow release of the slow-release material, and particularly can realize long-term and efficient remediation when being used for remediation of organic pollutants in soil and underground water.

Description

Technical Field

[0001] The present invention belongs to the technical field of sustained-release materials, and in particular relates to a method for preparing a sustained-release material, the prepared sustained-release material and applications thereof. Background Art

[0002] As the battle to protect the clean land continues to deepen, the problem of soil and groundwater pollutant remediation has gradually attracted the attention of researchers. Among them, organic pollutants present in industrial sites, such as trichloroethylene (TCE), tetrachloroethylene (PCE), and petroleum, will greatly damage the health of the ecosystem and cause great harm to humans and animals. At the same time, these pollutants are difficult to degrade under natural conditions, so it is extremely necessary to artificially remediate them. In situ chemical oxidation remediation (ISCO) is one of the commonly used remediation technologies in groundwater remediation due to its high remediation efficiency and small impact on contaminated sites.

[0003] Although chemical oxidation remediation is highly efficient, the oxidant cannot be released and stay underground for a long time, so the agent must be added continuously, which not only increases the cost of remediation but also aggravates the occurrence of secondary pollution. Therefore, it is necessary to develop methods that can achieve long-term remediation to achieve effective and stable remediation effects. Slow-release materials refer to materials that can be released continuously by extending the release time of reactants at a lower release rate. In the field of environmental remediation, slow-release materials are gradually applied to the field of groundwater remediation because they can achieve the goal of long-term effectiveness of the remediation process.

[0004] CN102491425A discloses a slow-release potassium permanganate oxidant for in-situ chemical remediation of groundwater. 4 Dispersed into molten paraffin, and then cooled and solidified in a mold to make sustained-release KMnO in different shapes 4 Oxidant, in order to achieve slow release of KMnO 4 The purpose of slow release of oxidants. However, in this study, harmful organic paraffin was used as one of the raw materials, which poses a great risk of secondary pollution.

[0005] CN107188361A discloses a slow-release sulfiding agent and a preparation method thereof, and a method for using the slow-release sulfiding agent to purify heavy metals and arsenic in an acidic solution. 2+ , Mn 2+ and Zn 2+ A sulfur source and a surfactant are added to the solution to react, and a nano-micron metal sulfide sol slow-release sulfiding agent is obtained, which is used to remove heavy metals and arsenic in acidic solutions. It has the advantages of high removal efficiency, low usage of sulfiding agent, and low release of hydrogen sulfide. However, this agent is only effective for heavy metal pollutants, and cannot repair organically contaminated groundwater, and it is difficult to achieve long-term repair.

[0006] CN114160558A discloses a contaminated soil in-situ chemical barrier material and its preparation and application. The material uses the in-situ clean soil of the site or the soil that meets the landfill disposal standard as the main matrix material, and adds clay minerals at the same time, which significantly reduces the permeability coefficient of the barrier mixture. In addition, the application of active materials in the mixture effectively controls and assists in reducing the pollution factors, thereby achieving the in-situ risk control and disposal goals of the contaminated site through a variety of functional characteristics. However, the material uses soil as the main matrix material. Experimental data show that soil and clay as matrix materials are very easy to absorb water, swell and disintegrate when exposed to water, which greatly reduces the release time of the active components in the material, and cannot achieve the purpose of slow release and long-term repair.

[0007] In summary, the slow-release remediation materials and remediation methods disclosed in the prior art are either only developed for heavy metal contaminated sites and have limited remediation effects on organic pollutants, or the base materials are not suitable for long-term release and the slow-release period is short, which makes it impossible to achieve the purpose of slow release and long-term remediation of slow-release materials. Therefore, it is urgent to develop an environmentally friendly, long-term release slow-release material. Summary of the invention

[0008] In view of the defects of the prior art, the present invention provides a method for preparing a slow-release material, a slow-release material prepared therefrom and its application. The slow-release material prepared by the method has the characteristics of environmental friendliness and long-term release, and can be used in the slow-release of slow-release materials, especially in the long-term and efficient repair of organic pollutants in soil and groundwater.

[0009] The first aspect of the present invention provides a method for preparing a sustained-release material. The method comprises:

[0010] (1) dispersing the first starch in water, then adding the first active substance, activated carbon, and sodium alginate and mixing them evenly to obtain product I;

[0011] (2) dispersing the second starch in water, and then adding the second active substance and mixing evenly to obtain product II;

[0012] (3) The product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent are mixed, molded, and dried to obtain a sustained-release material.

[0013] According to the present invention, the first starch in step (1) and / or the second starch in step (2) are modified porous starch. The first starch in step (1) and the second starch in step (2) can be the same starch or different starches.

[0014] According to the present invention, the preparation method of the modified porous starch comprises:

[0015] The porous starch is dispersed in water, octenyl succinic anhydride is added to react, the solid is filtered and dried to obtain the modified porous starch.

[0016] According to the present invention, in the preparation method of the modified porous starch, the porous starch is dispersed in water to obtain an emulsion, and the mass content of the porous starch is 25wt% to 40wt%.

[0017] According to the present invention, in the method for preparing the modified porous starch, the mass ratio of octenyl succinic anhydride to the porous starch is 1:(30-55).

[0018] According to the present invention, in the preparation method of the modified porous starch, the reaction conditions are: the reaction temperature is 40-55°C, the pH value of the reaction solution is controlled to be 8.5-10.5, and the reaction time is 2-6h. Further, the reaction is terminated by adjusting the pH value of the reaction solution to below 6. After the reaction is terminated, the product is washed, filtered and dried. The drying conditions are: temperature 45-55°C, time 10-16h.

[0019] According to the present invention, in the preparation method of the modified porous starch, the porous starch can be commercially available porous starch or homemade. In the porous starch, the median pore size is 4.5 to 6.5 μm. The modified porous starch has both hydrophilic and lipophilic properties. After being combined with activated carbon adsorption, it can not only help the activated carbon to be firmly combined with the inorganic oxidant, but also improve the hydrophilicity of the activated carbon itself to promote the entry of polluted water into the pores, helping to efficiently degrade pollutants.

[0020] According to the present invention, preferably, the porous starch preparation method can be prepared by conventional methods. Further, the porous starch preparation method comprises: adding α-amylase and saccharifying enzyme to a suspension of starch and water, filtering the obtained filter residue after reaction, and drying to obtain porous starch.

[0021] According to the present invention, in the method for preparing the porous starch, the starch includes one or more of corn starch, potato starch and cassava starch.

[0022] According to the present invention, in the method for preparing porous starch, the starch mass content in the suspension is 15wt% to 30wt%.

[0023] According to the present invention, in the method for preparing porous starch, the pH value of the suspension is 4.5-6.5.

[0024] According to the present invention, in the method for preparing porous starch, the suspension is preheated before adding α-amylase and saccharifying enzyme. The preheating temperature is 25 to 30° C. and the preheating time is 20 to 30 minutes.

[0025] According to the present invention, in the method for preparing porous starch, the reaction conditions are: temperature 30-40° C., time 33-35 minutes.

[0026] According to the present invention, in the method for preparing porous starch, the mass ratio of α-amylase to saccharifying enzyme is 1:(3.5-5.5).

[0027] According to the present invention, in the method for preparing porous starch, the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ to 0.11‰ of the mass of the suspension.

[0028] According to the present invention, in the method for preparing porous starch, the drying conditions are: drying at 45 to 55° C. for 16 to 24 hours.

[0029] According to the present invention, in step (1), the first active substance includes one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. Further, the microbial nutrient includes at least one of glucose, lignin, nitrate, and ferrous salt. The first active substance does not produce harmful substances after being oxidized, reduced, or biologically utilized, and does not cause secondary pollution of groundwater.

[0030] According to the present invention, the particle diameter of the activated carbon in step (1) is 40-60 mesh. The activated carbon is wood activated carbon and / or coal-made activated carbon. In the activated carbon, the pore volume occupied by macropores (pore diameter>50nm) is more than 5% of the total pore volume, preferably 5%-8%.

[0031] According to the present invention, in step (1), the materials are fed in the following ratio, i.e., the mass ratio of water, sodium alginate, first starch, first active substance, and activated carbon is 100: (1-3): (5-15): (35-50): (30-45). The product prepared within this ratio range can maximize the loading of the first starch particles carrying the first active substance in the pores of the activated carbon.

[0032] According to the present invention, in step (1), the first starch is dispersed in water and then stirred thoroughly. Then, the first active substance, activated carbon, and finally sodium alginate are added in order. Each time a material is added, it is mixed evenly. Preferably, after adding the activated carbon, stirring is performed, preferably mechanical stirring. The mechanical stirring device can be a magnetic stirrer. Preferably, the mechanical stirring time is 1 to 2.5 hours. More preferably, sodium alginate is added during stirring.

[0033] According to the present invention, in step (1), product I needs to be oscillated in a shaker. The oscillation time is 30 to 50 minutes, so that the starch with active substances is fully loaded onto the activated carbon. The obtained product I is an activated carbon composite material loaded with the first active substance.

[0034] According to the present invention, in step (1), product I can be filtered, washed, and dried. The drying can be natural drying, for example, drying at room temperature of 10 to 25 °C for 10 to 48 hours.

[0035] According to the present invention, in step (2), the second active substance includes one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrient agents, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate. Further, the microbial nutrient agent includes at least one of glucose, lignin, nitrate, and ferrous salt. After being redox or biologically utilized, the second active substance does not produce harmful substances and does not cause secondary pollution of groundwater. The first active substance and the second active substance can be the same or different.

[0036] According to the present invention, in step (2), the mass ratio of water, the second starch, and the second active substance is 100:(20 - 30):(50 - 60).

[0037] According to the present invention, in step (3), the strength agent includes at least one of quartz sand and glass fiber. The strength agent can provide mechanical strength for the slow-release material, and at the same time create large pores to improve the drug release rate. The matrix includes one or more of polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), and polypropylene (PP). The matrix serves as the matrix skeleton material of the slow-release material, playing a role in support and adhesion. The solvent includes at least one of dichloromethane and n-hexane. Preferably, the solvent includes dichloromethane and n-hexane. Preferably, the volume ratio of dichloromethane to n-hexane is 1:(0.5 - 1). The solvent will volatilize completely after the material is formed and does not exist in the material.

[0038] According to the present invention, in step (3), the mass ratio of product I, product II, strength agent, matrix, and solvent is (80 - 95):(75 - 85):(1 - 3):100:(50 - 70). This feeding ratio can make it form a layered wrapping structure, with the matrix material wrapped with the second active substance as the outer shell and the activated carbon composite material loaded with the first active substance as the inner core. In slow-release applications, a hierarchical release effect is further formed, prolonging the drug release time and increasing the oxidation cycle.

[0039] According to the present invention, preferably, in step (3), the mixing method of product I, product II, strength agent, matrix, and solvent includes:

[0040] (31) mixing a matrix with a solvent;

[0041] (32) the mixture obtained in step (31) is uniformly mixed with product I;

[0042] (33) The mixture obtained in step (32), product II and a strength agent are mixed uniformly.

[0043] According to the present invention, the shape of the sustained-release material in step (3) includes at least one of a cylindrical shape, a spherical shape, a strip shape and a compressed tablet shape.

[0044] According to the present invention, the drying conditions in step (3) are: temperature 30-45° C., time 30-60 hours.

[0045] The second aspect of the present invention provides a sustained-release material prepared by the above method.

[0046] The third aspect of the present invention provides an application of the sustained-release material prepared by the above method in sustained-release.

[0047] According to the present invention, the application includes the application of the slow-release material in remediating organic pollutants in groundwater.

[0048] According to the present invention, the application is to use the above-mentioned slow-release material as filler, fill it into permeable reaction walls, groundwater remediation wells and other remediation structures, and carry out in-situ chemical oxidation, in-situ chemical reduction and in-situ biological remediation of polluted groundwater. In the process of in-situ chemical oxidation and in-situ chemical reduction, when groundwater carries pollutants through the filler, it undergoes redox reaction with the active substances released by the above-mentioned slow-release material, so that the pollutants are removed and the groundwater is purified; in the process of in-situ biological remediation, the carbon source, nitrogen source, electron acceptor and other nutrients released by the slow-release material prepared by the above method provide continuous support for microbial agents, thereby accelerating the degradation of pollutants by microorganisms and achieving groundwater remediation.

[0049] Compared with the prior art, the present invention has achieved remarkable technical effects:

[0050] (1) In the method of the present invention, the method adopts a sequential batch mixing method to form a multi-layer wrapped multi-core structure of the sustained-release material. When the outer shell is completely decomposed, the multiple dispersed cores in the inner layer can release the active substance from the inner layer to the outer layer in relay, achieving the effect of layered multi-level release, thereby realizing long-term stable drug release.

[0051] Furthermore, in the method, the starch is modified with octenylsuccinic anhydride to make it have both hydrophilic and lipophilic properties. After being adsorbed and combined with activated carbon, it can not only help the activated carbon to firmly combine with the inorganic oxidant, but also improve the hydrophilicity of the activated carbon itself to promote the entry of polluted water into the pores, thereby helping the contact efficiency between high-efficiency pollutants and slow-release materials.

[0052] (2) The unique material ratio scheme in the product of the present invention ensures the loading amount of active substances while achieving close integration of active substances with other materials, develops a high-strength skeleton structure, avoids the material from breaking and disintegrating in water, and prolongs the classification speed of the finished material in water.

[0053] (3) The sustained-release material prepared by the method of the present invention can effectively prolong the release period of the agent and stabilize the release rate during application. In particular, when applied to the remediation of pollutants in groundwater, it can improve the removal efficiency of pollutants and the stability of technical operation, reduce the dosage of the agent, and prevent pollution rebound. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a diagram showing the sustained release performance test effect of Example 1;

[0055] Figure 2 This is a diagram showing the sustained release performance test effect of Example 2;

[0056] Figure 3 This is a diagram showing the sustained release performance test effect of Example 3;

[0057] Figure 4 This is a graph showing the sustained release performance test effect of Comparative Example 1;

[0058] Figure 5 A schematic diagram of a contaminated groundwater treatment device for an application example;

[0059] Figure 6 This is an application example of the remediation effect of slow-release materials on groundwater contaminated by petroleum hydrocarbons (TPH). DETAILED DESCRIPTION

[0060] The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited by the examples.

[0061] In the present invention, the method for testing the sustained-release performance is: weigh 10g of the sustained-release material and place it in 1L of deionized water, and measure the content of the active substance in the water at regular intervals, and at the same time measure the level of organic matter in the water to detect whether the sustained-release material will cause secondary pollution of the water body. The test interval increases with the test time. For example, the test can be performed every 1 day in the initial stage, every 2 to 5 days in the middle stage, and every 10 days in the final stage. After each test, the deionized water that has been tested is replaced with fresh 1L of deionized water. Repeat the above steps regularly until the active substance cannot be detected in the deionized water. In the present invention, the content of the active substance in the water is tested by spectrophotometry. For example, in each case, when persulfate is used as the active substance, the test method for the persulfate content adopts the potassium iodide-ultraviolet spectrophotometry method. When ferrous salt is used as the active substance, the test method for the iron content adopts the o-phenanthroline spectrophotometry method. When glucose is used as the active substance, the glucose determination method is sampled by high-performance liquid chromatography.

[0062] In the present invention, the test method for organic matter in water adopts the method of "Determination of Volatile Organic Matter in Water Quality - Purge and Trap-Gas Chromatography (HJ 686-2014)".

[0063] In the present invention, the loading amount of active substances in the sustained-release materials prepared in each example is determined by an element analyzer. In the present invention, the release period is the time from the addition of the sustained-release material to the water until the active substances can no longer be detected in the water; the cumulative release rate of the sustained-release material is the sum of the mass of active substances measured each time during the release period, divided by the loading amount of active substances in the sustained-release material; the average release rate is the sum of the mass of active substances measured each time during the release period, divided by the release period.

[0064] Example 1

[0065] (1) The preparation method of modified porous starch is:

[0066] Preparation of porous starch: Add corn starch to water and stir evenly to form a 30wt% starch suspension with a pH of 5.5. Preheat the suspension in a water bath for 30 minutes at a temperature of 30°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:5.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.11‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 40°C and keep the reaction for 33 minutes. After filtering the reaction mixture to remove water, place it in a 45°C oven and dry it for 24 hours to obtain porous starch. The median pore size of the porous starch is 6.5μm.

[0067] Preparation of modified porous starch: The porous starch prepared as above was used as a raw material, water was added to prepare a 40wt% starch emulsion, octenyl succinic anhydride was added, the mass ratio of octenyl succinic anhydride to the porous starch in the starch emulsion was 1:55, the reaction was maintained at a constant temperature of 55°C in a water bath for 3h, and the pH of the reaction solution was controlled to be 9. Then, hydrochloric acid was added to adjust the pH to 6 to terminate the reaction. The reaction product was washed, filtered, and dried at 50°C for 13h to obtain modified porous starch.

[0068] In this example, both the first starch and the second starch are the modified porous starch mentioned above.

[0069] 15g of the first starch was added to 100g of water, and the mixture was stirred and mixed to form an emulsion. Then 50g of sodium persulfate was added to the emulsion to dissolve and mix. After stirring, 45g of 60-mesh wood activated carbon (the pore volume occupied by macropores was 5.3% of the total pore volume) was added to the mixture, and the mixture was placed in a magnetic stirrer and stirred for 2h. Then 3g of sodium alginate was added while stirring to form a colloid, and the colloid was placed in a shaking table and shaken for 45min, so that the starch with active substances was fully loaded into the activated carbon. Then the activated carbon after adsorption was filtered, washed, and air-dried at 25°C for 48h to obtain product I, i.e., an activated carbon composite material.

[0070] (2) Re-weigh some of the modified porous starch as the second starch and sodium persulfate, mix the starch and sodium persulfate in water to obtain product II. The mass ratio of the feed materials is water: starch: sodium persulfate = 100:30:60.

[0071] (3) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0072] (31) mixing the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:1);

[0073] (32) the mixture obtained in step (31) is uniformly mixed with product I;

[0074] (33) The mixture obtained in step (32), product II and strength agent quartz sand are fully mixed. The ratio of product I: product II: quartz sand: polytetrafluoroethylene: solvent is 95:85:3:100:70. After fully mixing, the material is extruded into strips, and dried at 45°C for 48 hours to obtain cylindrical granular sustained-release material A.

[0075] It was determined that the mass fraction of sulfur in the slow-release material A in this example was 5.94wt%, and the loading amount of sodium persulfate in the slow-release material A was calculated to be 22.09wt%. The slow-release performance test results of the slow-release material in this example are as follows: Figure 1As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 14 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 15 to 135 days, which is the sustained release stage of the inner core, characterized by a stable release rate and a smooth curve; the relay release of the first and second stages achieves the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material A is 135 days. The cumulative release rate of sodium persulfate during the release period is 97.9wt%, and the average release rate is 1.7mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0076] At the same time, the inventor replaced the first starch and the second starch in this example with ordinary corn starch as raw materials, conducted parallel comparative experiments, and prepared a sustained-release material DA. It was determined that the mass fraction of sulfur in the sustained-release material DA was 4.69wt%, and the calculated loading amount of sodium persulfate in the sustained-release material A was 17.51wt%. The release period of the sustained-release material DA was 80 days. The cumulative release rate of sodium persulfate during the release period was 96wt%, and the average release rate was 2.2mg / (gd). The test results of the sustained-release material A and the sustained-release material DA were compared to show that the use of modified porous starch as raw material further extended the release period of the medicament, and the release rate was more stable.

[0077] Example 2

[0078] (1) The preparation method of modified porous starch is:

[0079] Preparation of porous starch: Add potato starch to water and stir evenly to form a 15wt% starch suspension with a pH of 4.5. Preheat the suspension in a water bath for 20 minutes at a temperature of 25°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:3.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.07‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 35°C and keep the reaction for 33 minutes. After filtering the reacted mixture to remove water, place it in a 55°C oven and dry it for 20 hours to obtain porous starch. The median pore size of the porous starch is 4.5μm.

[0080] Preparation of modified porous starch: Using the porous starch prepared above as raw material, add water to prepare a 25wt% starch emulsion, add octenyl succinic anhydride, the mass ratio of octenyl succinic anhydride to the porous starch in the starch emulsion is 1:30, keep the reaction at a constant temperature of 50°C in a water bath for 3 hours, and control the pH of the reaction solution to 10.5. Then, add hydrochloric acid to adjust the pH to 6 to terminate the reaction. Wash the reaction product, filter it, and dry it at 55°C for 10 hours to obtain modified porous starch.

[0081] In this example, both the first starch and the second starch are the modified porous starch mentioned above.

[0082] 5g of the first starch was added to 100g of water, and the mixture was stirred and mixed to form an emulsion. Then 35g of potassium persulfate was added to the emulsion to dissolve and mix. After stirring, 30g of 40-mesh wood activated carbon (the pore volume occupied by macropores was 7.8% of the total pore volume) was added to the mixture, and the mixture was placed in a magnetic stirrer and stirred for 1h. Then 1g of sodium alginate was added while stirring to form a colloid, and the colloid was placed in a shaking table and shaken for 30min, so that the starch with active substances was fully loaded into the activated carbon. Then the activated carbon after adsorption was filtered, washed, and air-dried at 25°C for 24h to obtain product I, i.e., an activated carbon composite material.

[0083] (2) Re-weigh some of the modified starch as the second starch and calcium persulfate, and mix the starch and calcium persulfate in water to obtain product II. The mass ratio of the feed materials is water: starch: calcium persulfate = 100:20:50.

[0084] (3) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0085] (31) mixing the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:0.5);

[0086] (32) the mixture obtained in step (31) is uniformly mixed with product I;

[0087] (33) The mixture obtained in step (32), product II and strength agent quartz sand are fully mixed. The ratio of product I: product II: quartz sand: polytetrafluoroethylene: solvent is 80:75:1:100:50. After fully mixing, the material is extruded into strips, and dried at 40°C for 60 hours to obtain cylindrical granular sustained-release material B.

[0088] The mass fraction of sulfur in the sustained-release material B in this example is determined to be 5.38 wt %, and the loading amount of active substances (potassium persulfate and calcium persulfate) in the sustained-release material B is calculated to be 20.58 wt %. The sustained-release performance test results of the sustained-release material in this example are shown in FIG. Figure 2As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 7 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 8 to 132 days, which is the sustained release stage of the inner core, characterized by a stable release rate and a smooth curve; the relay release of the first and second stages achieves the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material B is 132 days. The cumulative release rate of sodium persulfate during the release period is 95.9wt%, and the average release rate is 1.73mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0089] Example 3

[0090] (1) The preparation method of modified porous starch is:

[0091] Preparation of porous starch: Add cassava starch to water and stir evenly to make a 25wt% starch suspension with a pH of 6.5. Preheat the suspension in a water bath for 25 minutes at a temperature of 28°C. Then, add a mixture of α-amylase and saccharifying enzyme in a mass ratio of 1:4.5 to the starch suspension, and the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ of the mass of the suspension. Keep the suspension in a water bath at a constant temperature of 30°C and keep the reaction for 35 minutes. After filtering the reacted mixture to remove water, place it in a 50°C oven and dry it for 24 hours to obtain porous starch. The median pore size of the porous starch is 5.5μm.

[0092] Preparation of modified porous starch: Using the porous starch prepared above as raw material, add water to prepare a 35wt% starch emulsion, add octenyl succinic anhydride, the mass ratio of octenyl succinic anhydride to the porous starch in the starch emulsion is 1:45, keep the reaction at a constant temperature of 40°C in a water bath for 3h, and control the pH of the reaction solution to 8.5. Then, add hydrochloric acid to adjust the pH to 6 to terminate the reaction. Wash the reaction product, filter it, and dry it at 45°C for 16h to obtain the modified porous starch.

[0093] In this example, both the first starch and the second starch are the modified porous starch mentioned above.

[0094] 10g of the first starch was added to 100g of water, and the mixture was stirred and mixed to form an emulsion. Then 40g of ferrous sulfate was added to the emulsion to dissolve and mix. After stirring, 40g of 50-mesh wood activated carbon (the pore volume occupied by macropores was 6.7% of the total pore volume) was added to the mixture, and the mixture was placed in a magnetic stirrer and stirred for 1.5h. Then 2g of sodium alginate was added while stirring to form a colloid, and the colloid was placed in a shaking table and vibrated for 50min, so that the starch with active substances was fully loaded into the activated carbon. Then the activated carbon after adsorption was filtered, washed, and air-dried at 25°C for 48h to obtain product I, i.e., an activated carbon composite material.

[0095] (2) Reweighing Some of the modified starch as the second starch and ferrous sulfate were reweighed, and the starch and ferrous sulfate were mixed in water to obtain product II. The mass ratio of the feed materials was water: starch: ferrous sulfate = 100: 25: 55.

[0096] (3) Mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, and forming and drying them to obtain a sustained-release material. The specific steps are:

[0097] (31) mixing the matrix polytetrafluoroethylene powder with a solvent (dichloromethane and n-hexane in a volume ratio of 1:0.8);

[0098] (32) the mixture obtained in step (31) is uniformly mixed with product I;

[0099] (33) The mixture obtained in step (32), product II and strength agent quartz sand are fully mixed. The ratio of product I: product II: quartz sand: polytetrafluoroethylene: solvent is 85:80:2:100:60. After fully mixing, the material is extruded into strips, and dried at 45°C for 60 hours to obtain cylindrical granular sustained-release material C.

[0100] It was determined that the mass fraction of iron in the sustained-release material C in this example was 8.6 wt %, and the loading amount of ferrous sulfate in the sustained-release material C was calculated to be 23.34 wt %. The sustained-release performance test results of the sustained-release material in this example are shown in FIG. Figure 3 As shown, it can be seen that the release of active substances can be divided into two stages: the first stage is from 0 to 12 days, which is the decomposition and release stage of the outer shell, characterized by a faster change in release rate and a steeper release curve; the second stage is from 13 to 130 days, which is the sustained release stage of the inner core, characterized by a stable release rate and a smooth curve; the relay release of the first and second stages achieves the effect of layered multi-level sustained release. The final test results show that the release period of sustained-release material C is 130 days. The cumulative release rate of sodium persulfate during the release period is 96.5wt%, and the average release rate is 1.73mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0101] Example 4

[0102] The difference from Example 1 is that the active substances in steps (1) and (2) are both glucose, and the rest is the same as Example 1.

[0103] The measured results show that the glucose loading in the sustained-release material D is 28.42 wt %. Figure 1The release of the active substance in this example can be divided into two stages: the first stage is from 0 to 6 days, which is the decomposition and release stage of the outer shell, characterized by a rapid change in release rate and a steep release curve; the second stage is from 7 to 132 days, which is the sustained release stage of the inner core, characterized by a stable release rate and a smooth curve; the relay release of the first and second stages achieves a layered multi-level sustained release effect. The final test results show that the release period of sustained-release material D is 132 days. The cumulative release rate of sodium persulfate during the release period is 95wt%, and the average release rate is 1.75mg / (gd). During the entire sustained-release period, no organic matter was detected in the water, and the particles of the sustained-release material were never broken or disintegrated.

[0104] Comparative Example 1

[0105] The difference between this example and Example 1 is that the active substance sodium persulfate is not added in steps, but all at once. That is, all the materials in steps (1) and (2) of Example 1 are added at once in step (1) of Example 1. The material feeding amount and other operation steps are the same as in Example 1.

[0106] After determination, the sustained release performance test results of this example sustained release material are as follows Figure 4 As shown, the results showed that the release period of the sustained-release material was only 9 days, and the slow-release effect was not achieved.

[0107] Application Examples

[0108] The principle of using slow-release materials to repair contaminated groundwater is as follows Figure 5 As shown, the slow-release material A of Example 1 of the present invention is used as a filler and filled into a permeable reaction wall, and the permeable reaction wall is arranged in the flow path of organic contaminated groundwater. The contaminated groundwater penetrates through the wall, and the organic pollutants are oxidized and degraded by the active substances released by the slow-release material, and the pollutants are removed. The pollution removal rate can be calculated by testing the pollutant concentrations in the groundwater upstream and downstream of the permeable reaction wall respectively. In this application example, groundwater contaminated by petroleum hydrocarbons (TPH) was selected, and the concentration of influent petroleum hydrocarbons was (120±5) mg / L. The wall size was set to 10m*0.6m*5.8m, and 1.9 tons of slow-release material was filled as the wall filler at one time, and a pollution remediation application lasting 145 days was carried out. During this period, the TPH concentrations in the groundwater upstream and downstream of the permeable reaction wall were measured at regular intervals, and the pollution removal rate was calculated. The pollution remediation effect is shown in the figure. Figure 6 As shown. Within the 0th to 135th day, the TPH removal rate was maintained above 90wt%, and the highest could reach 97wt%. After the 135th day, most of the oxidants in the slow-release material had been released, and the pollution removal rate changed from high to low. This result shows that the slow-release performance of the slow-release material is stable, and the material can be continuously released within the slow-release period, successfully repairing the contaminated groundwater.

Claims

1. A method for preparing a sustained-release material, It is characterized in that The method comprises: (1) dispersing the first starch in water, then adding the first active substance, activated carbon, and sodium alginate and mixing them evenly to obtain product I; (2) dispersing the second starch in water, and then adding the second active substance and mixing evenly to obtain product II; (3) mixing the product I obtained in step (1), the product II obtained in step (2), a strength agent, a matrix, and a solvent, molding, and drying to obtain a sustained-release material; The first starch in step (1) and / or the first starch in step (2) is a modified porous starch.

2. The method according to claim 1, It is characterized in that The preparation method of the modified porous starch comprises: dispersing the porous starch in water, adding octenyl succinic anhydride to react, filtering to obtain a solid, and drying to obtain the modified porous starch.

3. The method according to claim 2, It is characterized in that In the preparation method of the modified porous starch, the mass ratio of octenyl succinic anhydride to porous starch is 1:(30-55).

4. The method according to claim 2, It is characterized in that In the preparation method of the modified porous starch, the reaction conditions are: the reaction temperature is 40 to 55° C.; and / or the pH value of the reaction solution is controlled to be 8.5 to 10.5; and / or the reaction time is 2 to 6 hours.

5. The method according to claim 1 or 2, It is characterized in that In the porous starch, the median pore diameter is 4.5 to 6.5 μm.

6. The method according to claim 1 or 2, It is characterized in that The method for preparing porous starch comprises: adding α-amylase and saccharifying enzyme to a suspension of starch and water, filtering and drying the filter residue obtained after the reaction, and obtaining porous starch.

7. The method according to claim 6, It is characterized in that In the method for preparing porous starch, the reaction conditions are: temperature 30-40°C, time 33-35 minutes; and / or, the mass ratio of α-amylase to saccharifying enzyme is 1:(3.5-5.5); and / or, the total amount of α-amylase and saccharifying enzyme added accounts for 0.03‰ to 0.11‰ of the mass of the suspension; And / or, the starch content in the suspension is 15wt% to 30wt%.

8. The method according to claim 1, It is characterized in that In step (1), the first active substance comprises one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate; Furthermore, the microbial nutrient includes at least one of glucose, lignin, nitrate and ferrous salt.

9. The method according to claim 1, It is characterized in that In step (1), the materials are fed in the following ratio, i.e., the mass ratio of water, sodium alginate, the first starch, the first active substance, and activated carbon is 100: (1-3): (5-15): (35-50): (30-45).

10. The method according to claim 1, It is characterized in that In step (2), the second active substance comprises one or more of sodium persulfate, potassium persulfate, ammonium persulfate, calcium persulfate, potassium permanganate, sodium permanganate, sodium sulfite, and microbial nutrients, preferably one or more of sodium persulfate, potassium persulfate, and ammonium persulfate; Furthermore, the microbial nutrient includes at least one of glucose, lignin, nitrate and ferrous salt.

11. The method according to claim 1, It is characterized in that In step (2), the mass ratio of water, the second starch and the second active substance is 100:(20-30):(50-60).

12. The method according to claim 1, It is characterized in that In step (3), the mass ratio of product I, product II, strength agent, matrix and solvent is (80-95):(75-85):(1-3):100:(50-70).

13. A sustained-release material prepared by the method according to any one of claims 1 to 12.

14. Use of a sustained-release material prepared by the method according to any one of claims 1 to 12 in sustained-release of materials.

Images