A granular persulfate slow-release material, a preparation method and application thereof

Abstract

The application discloses granular persulfate slow-release material and a preparation method and application thereof, and belongs to the technical field of groundwater remediation. The granular persulfate slow-release material has a core-shell structure; the core-shell structure comprises an outer shell and an inner core, wherein the outer shell is composed of stearic acid, and the inner core is composed of persulfate and stearic acid. The preparation method is as follows: after the stearic acid is melted and mixed with the persulfate, the mixture is obtained after stirring and cooling; the mixture is ground and sieved, and then added into a granulator, and the melted stearic acid is added twice for granulation, so that the granular persulfate slow-release material is obtained. The application overcomes the problems of the prior art, such as the fast consumption of persulfate and the reverse diffusion of pollutants, realizes the long-acting and stable release of the persulfate, and further effectively and durably performs in-situ chemical oxidation remediation on the groundwater.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of groundwater remediation, and particularly relates to a granular persulfate slow-release material and a preparation method and application thereof. BACKGROUND

[0002] Chemical oxidation remediation technology includes ex-situ remediation and in-situ remediation, wherein the former draws contaminated groundwater to the ground surface and injects it back to the ground after chemical oxidation treatment, and the latter directly injects oxidants into the contaminated site to degrade pollutants by the oxidizing property of the oxidants. Ex-situ remediation can damage the groundwater environment, has high cost and high difficulty in facility construction, while in-situ remediation is directly remediated and treated on the contaminated site, has low cost and does not affect the surrounding ecological environment.

[0003] In in-situ chemical oxidation remediation of groundwater, commonly used oxidants include permanganate (MnO4 - ), Fenton reagent (H2O2), ozone (O3) and persulfate (S2O8 2- ). The oxidation-reduction potentials of the oxidants themselves and the active substances generated by their excitation are MnO4 - (1.69V) < H2O2(1.77V) < S2O8 2- (2.01V) < O3(2.07V) < SO4· - (2.6V) < ·OH(2.8V). S2O8 2- Because of the characteristics of higher oxidation-reduction potential, longer time in the natural environment, longer half-life of SO4· - generated by activation than ·OH, etc., it has attracted much attention.

[0004] However, in the prior art, direct injection of persulfate for in-situ chemical oxidation remediation has problems such as rapid consumption of persulfate and reverse diffusion of pollutants, so it is necessary to combine slow-release technology to realize long-term and stable release of oxidants.

[0005] Therefore, how to provide a slow-release material capable of realizing long-term and stable release of persulfate and effectively and durably performing in-situ chemical oxidation remediation of groundwater is a technical problem that those skilled in the art need to solve. SUMMARY

[0006] In view of the problems in the prior art, the application provides a granular persulfate slow-release material and a preparation method and application thereof, which overcomes the problems of rapid consumption of persulfate and reverse diffusion of pollutants in the prior art, realizes long-term and stable release of persulfate, and effectively and durably performs in-situ chemical oxidation remediation of groundwater.

[0007] To achieve the above purpose, the application provides the following technical solutions:

[0008] The present invention provides a granular persulfate slow-release material having a core-shell structure; the core-shell structure includes an outer shell and an inner core, wherein the outer shell is composed of stearic acid and the inner core is composed of persulfate and stearic acid.

[0009] Stearic acid is an organic compound with the chemical formula C. 17 H 35 CO2H. Stearic acid is a saturated fatty acid with an 18-carbon chain. Its IUPAC name is octadecanoic acid. This acid is a white, waxy substance.

[0010] Persulfate oxidation is a chemical reaction that uses persulfate as a catalyst and oxygen as an oxygen source. Persulfate forms covalent bonds with the oxidized molecule, creating new ligands. This alters the molecular structure of the oxidized molecule, making it more susceptible to oxidation by oxygen centers, resulting in the production of water-soluble active ions that facilitate the reaction. However, the reaction rate of persulfate is very fast. Even when encapsulated in slow-release materials, it is prone to problems such as a "burst release" in the early stages and insufficient release performance in the later stages.

[0011] The presence of the outer shell in the core-shell structure allows the active substances (persulfate) in the inner core to be released slowly, thus achieving a longer release lifespan and enabling sustained and effective in-situ chemical oxidation remediation of groundwater.

[0012] Preferably, the raw materials include the following parts by weight: 4.6 to 5.2 parts stearic acid and 1 to 1.6 parts persulfate. Beneficial effects: When the amount of persulfate in the core exceeds 1.6 parts, the slow release rate of the persulfate is too fast, exhibiting a "burst release" effect; when the amount of persulfate in the core is less than 1 part, the slow release rate of the persulfate is too slow, making it difficult to meet the requirements of practical applications.

[0013] Preferably, the persulfate has a particle size of 80-100 mesh; the persulfate includes sodium persulfate and / or potassium persulfate.

[0014] Preferably, the stearic acid has a melting point of 67–70°C and a residue on ignition of ≤0.2%.

[0015] Preferably, the sodium persulfate release rate in the granular persulfate slow-release material is 1–19 mg / (d·g).

[0016] Preferably, the sustained-release life of the granular persulfate slow-release material is 21 to 65 days.

[0017] Preferably, the particle size of the granular persulfate slow-release material is 5-10 mm.

[0018] Beneficial effects: The technical solution of this invention can control the slow-release life, slow-release amount and slow-release rate of sodium persulfate in sodium persulfate slow-release material by adjusting the ratio of stearic acid and sodium persulfate and the particle size, so as to adapt to groundwater remediation projects with different pollution levels.

[0019] Another object of the present invention is to provide a method for preparing granular persulfate sustained-release material, comprising the following steps:

[0020] (1) Heat stearic acid until it melts, then mix it with persulfate, stir and cool to obtain a mixture;

[0021] (2) After grinding and sieving the mixture, add it to the granulator. When the rotation speed of the turntable reaches 15 r / min, add molten stearic acid as a binder to granulate and obtain a semi-finished product.

[0022] (3) Put the semi-finished product into a granulator, add melted stearic acid again to granulate, and obtain granulated persulfate slow-release material.

[0023] Preferably, the stearic acid in step (1) is 3.1 to 3.5 parts by weight, and the persulfate is 1 to 1.6 parts by weight.

[0024] Preferably, the amount of melted stearic acid added in step (2) is 1.2 to 1.3 parts by weight.

[0025] Preferably, the amount of melted stearic acid added in step (3) is 0.3 to 0.4 parts by weight.

[0026] Preferably, the heating process described in step (1) to melt is a constant temperature water bath heating at 75°C.

[0027] Preferably, the stirring temperature is 35-40°C and the stirring speed is 100-150 r / min; the cooling is natural cooling to room temperature.

[0028] Preferably, the particle size of the grinding in step (2) is 40 to 60 mesh.

[0029] Preferably, the angle range of the granulator during granulation in steps (2) and (3) is 40 to 65° and the temperature is 50 to 60°.

[0030] Another objective of this invention is to provide an application of granular persulfate slow-release material in in-situ chemical oxidation remediation of groundwater.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] (1) This invention is the first to combine granulation technology and slow-release technology to prepare a granular persulfate slow-release material. The preparation method is simple and easy to operate.

[0033] (2) This invention controls the release life, release amount and release rate of sodium persulfate in sodium persulfate slow-release material by adjusting the ratio of stearic acid and sodium persulfate and the particle size, so as to adapt to groundwater remediation projects with different pollution levels.

[0034] (3) The materials used in this invention are clean and environmentally friendly and will not cause pollution to the environment. Moreover, the slow-release materials are easy to replace after they reach their slow-release lifespan. Attached Figure Description

[0035] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0036] Fig. 1 The image shows a SEM image of the surface of the granular persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2 before leaching with deionized water at a magnification of 50x.

[0037] Fig. 2 The image shows a cross-section of the granular persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2, before being leached with deionized water, under a magnification of 5000x.

[0038] Fig. 3 The image is a SEM image at 50x magnification of the surface of the granular persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2 after leaching with deionized water.

[0039] Fig. 4 The image shows a cross-section of the granular persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2 after leaching with deionized water and magnification at 5000x.

[0040] Fig. 5 Release curves of granular sulfate slow-release materials of different particle sizes prepared in Examples 1-3 in sealed brown glass bottles;

[0041] Fig. 6 The graphs show the release curves of column experiments for granular persulfate slow-release materials of different particle sizes prepared in Examples 1-3. Detailed Implementation

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0046] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0047] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0048] All raw materials used in the following embodiments of the present invention are commercially available.

[0049] The following embodiments are further illustrations of the technical solution of the present invention.

[0050] The present invention provides a granular persulfate slow-release material having a core-shell structure; the core-shell structure includes an outer shell and an inner core, wherein the outer shell is composed of stearic acid and the inner core is composed of persulfate and stearic acid.

[0051] In some embodiments of the present invention, the granular persulfate slow-release material preferably contains the following parts by weight of raw materials: stearic acid preferably 4.6 to 5.2 parts, more preferably 4.8 parts in the embodiments; persulfate 1 to 1.6 parts, more preferably 1.6 parts in the embodiments.

[0052] In some embodiments of the present invention, the particle size of the persulfate is preferably 80-100 mesh, more preferably 100 mesh as in the embodiments of the present invention; the types of persulfate include sodium persulfate and / or potassium persulfate, and more preferably sodium persulfate as in the embodiments.

[0053] In some embodiments of the present invention, the preferred melting point of stearic acid is 67-70°C, and the amount of stearic acid residue on ignition is ≤0.2%.

[0054] In some embodiments of the present invention, the sodium persulfate release rate in the granular persulfate slow-release material is 1–19 mg / (d·g).

[0055] In some embodiments of the present invention, the sustained-release life of the persulfate sustained-release material is 21 to 65 days.

[0056] In some embodiments of the present invention, the particle size of the granular persulfate slow-release material is 5-10 mm.

[0057] This invention provides a method for preparing granular persulfate sustained-release material, comprising the following steps:

[0058] (1) Heat stearic acid until it melts, then mix it with persulfate, stir and cool to obtain a mixture;

[0059] (2) After grinding and sieving the mixture, add it to the granulator. When the rotation speed of the turntable reaches 15 r / min, add molten stearic acid as a binder to granulate and obtain a semi-finished product.

[0060] (3) Put the semi-finished product into a granulator, add melted stearic acid again to granulate, and obtain granulated persulfate slow-release material.

[0061] In some embodiments of the present invention, the weight of stearic acid in step (1) is preferably 3.1 to 3.5 parts, more preferably 3.2 parts in the embodiments; the weight of persulfate is preferably 1 to 1.6 parts, more preferably 1.6 parts in the embodiments.

[0062] In some embodiments of the present invention, the amount of molten stearic acid added in step (2) is preferably 1.2 to 1.3 parts by weight, and more preferably 1.2 parts as in the embodiments.

[0063] In some embodiments of the present invention, the amount of molten stearic acid added in step (3) is 0.3 to 0.4 parts by weight, more preferably 0.4 parts in the embodiments.

[0064] In some embodiments of the present invention, the heating process described in step (1) to melt is preferably a constant temperature water bath heating at 75°C.

[0065] In some embodiments of the present invention, the stirring temperature is preferably 35-40°C, more preferably 35°C in the embodiments; the stirring speed is preferably 100-150 r / min, more preferably 120 r / min in the embodiments; and the cooling is natural cooling to room temperature.

[0066] In some embodiments of the present invention, the particle size of the grinding in step (2) is preferably 40 to 60 mesh, and more preferably 60 mesh in the embodiments.

[0067] In some embodiments of the present invention, the angle range of the granulator during granulation in step (2) is 40 to 65°, more preferably 5° in the embodiments; the temperature is 50 to 60°, more preferably 50° in the embodiments.

[0068] In some embodiments of the present invention, the angle range of the granulator during granulation in step (3) is 40 to 65°, more preferably as in the embodiments; the temperature is 50 to 60°C, more preferably 50°C as in the embodiments.

[0069] The granular persulfate slow-release material of the present invention can be applied to in-situ chemical oxidation remediation of groundwater.

[0070] Example 1

[0071] (1) 3.2 parts of stearic acid (melting point 67-70℃, residue on ignition ≤0.2%) were heated in a water bath at 75℃ and then mixed with 1.6 parts of persulfate (particle size 100 mesh). The mixture was stirred and cooled on a magnetic stirrer (magnetic stirrer speed 120r / min, temperature 35℃) to obtain the mixture.

[0072] (2) After grinding and sieving the mixture (particle size of 60 mesh), add it to the granulator (adjust the disc angle to 52° and the temperature to 50°). When the disc speed reaches 15 r / min, add 1.2 parts of melted stearic acid for the first time to granulate and obtain a semi-finished product.

[0073] (3) Place the semi-finished product into a granulator (adjust the disc angle to 52° and the temperature to 50°C), add 0.4 parts of melted stearic acid again for granulation, and obtain the granular persulfate slow-release material product with a particle size of 5 mm.

[0074] Example 2

[0075] (1) 3.2 parts of stearic acid (melting point 67-70℃, residue on ignition ≤0.2%) were heated in a water bath at 75℃ and then mixed with 1.6 parts of persulfate (particle size 100 mesh). The mixture was stirred and cooled on a magnetic stirrer (magnetic stirrer speed 120r / min, temperature 35℃) to obtain the mixture.

[0076] (2) After grinding and sieving the mixture (particle size of 60 mesh), add it to the granulator (adjust the disc angle to 47° and the temperature to 50°). When the disc speed reaches 15 r / min, add 1.2 parts of melted stearic acid for the first time to granulate and obtain a semi-finished product.

[0077] (3) Place the semi-finished product into a granulator (adjust the disc angle to 47° and the temperature to 50°C), add 0.4 parts of melted stearic acid again for granulation, and obtain the granular persulfate slow-release material product with a particle size of 7.5 mm.

[0078] Example 3

[0079] (1) 3.2 parts of stearic acid (melting point 67-70℃, residue on ignition ≤0.2%) were heated in a water bath at 75℃ and then mixed with 1.6 parts of persulfate (particle size 100 mesh). The mixture was stirred and cooled on a magnetic stirrer (magnetic stirrer speed 120r / min, temperature 35℃) to obtain the mixture.

[0080] (2) After grinding and sieving the mixture (particle size of 60 mesh), add it to the granulator (adjust the disc angle to 40° and the temperature to 50°). When the disc speed reaches 15 r / min, add 1.2 parts of melted stearic acid for the first time to granulate and obtain a semi-finished product.

[0081] (3) Place the semi-finished product into a granulator (adjust the disc angle to 40° and the temperature to 50°C), add 0.4 parts of melted stearic acid again for granulation, and obtain the granular persulfate slow-release material product with a particle size of 10 mm.

[0082] The granular persulfate slow-release material of the present invention was characterized in terms of structure and performance by the following means:

[0083] Figs. 1-2 The image shows the SEM characterization of the surface of the granular persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2 before release at different magnifications. Figs. 3-4 The image shows the SEM characterization of the surface of the persulfate slow-release material with a particle size of 7.5 mm prepared in Example 2 after release at different magnifications. Analysis shows that the granular persulfate slow-release material has small and few pores on its surface before release, while after leaching, the surface of the slow-release material has large and numerous pores. This is because the stearic acid on the surface of the slow-release material creates pores under the erosion of water, allowing the sodium persulfate inside to be gradually released.

[0084] The granular persulfate slow-release materials of different particle sizes prepared in Examples 1 to 3 were added to sealed brown glass bottles with a water-to-solid ratio of 30:1. The content of sodium persulfate in the leachate was tested periodically. The sodium persulfate concentration was detected by iodometric titration and measured at 400 nm using an ultraviolet spectrophotometer. Fig. 5 The figures show the release curves of sulfate sustained-release materials with different particle sizes prepared in Examples 1-3 in sealed brown glass bottles. Analysis shows that the sustained-release materials prepared in the examples of this invention all have a sustained-release capability. Furthermore, the sustained-release lifetimes of the three particle size sustained-release materials are 36, 45, and 65 days, respectively, and the average release rates of sodium persulfate are 7, 6, and 4 mg / d / g, respectively.

[0085] 32g of granular persulfate slow-release material with different particle sizes (5, 7.5, 10mm) prepared in Examples 1-3 were alternately stacked and filled into an organic glass bead column with a length of 180mm, an inner diameter of 30mm, and an outer diameter of 40mm. Deionized water was injected from the bottom of the column and flowed out from the top using a peristaltic pump at a flow rate of 1mL / min. The persulfate concentration in the effluent was monitored at different time intervals. Fig. 6 The figures show the release curves of granular persulfate slow-release materials with different particle sizes prepared in Examples 1-3, as shown in column experiments. The results indicate that the slow-release lifetimes of the three particle size slow-release materials are 21, 28, and 28 days, respectively, and the average release rates of sodium persulfate are 9, 7, and 5 mg / d / g, respectively.

[0086] Example 4

[0087] (1) 3.1 parts of stearic acid (melting point 67-70℃, residue on ignition ≤0.2%) were heated in a water bath at 75℃ and then mixed with 1 part of persulfate (particle size 80 mesh). The mixture was stirred and cooled on a magnetic stirrer (magnetic stirrer speed 100r / min, temperature 37℃) to obtain the mixture.

[0088] (2) After grinding and sieving the mixture (particle size of 40 mesh), add it to the granulator (adjust the disc angle to 47° and the temperature to 55°). When the disc speed reaches 15 r / min, add 1.3 parts of melted stearic acid for the first time to granulate and obtain a semi-finished product.

[0089] (3) Place the semi-finished product into a granulator (adjust the disc angle to 47° and the temperature to 55°C), add 0.4 parts of melted stearic acid again for granulation, and obtain the persulfate slow-release material finished product with a particle size of 7.5 mm.

[0090] Example 5

[0091] (1) Heat 3.5 parts of stearic acid (melting point 67-70℃, residue on ignition ≤0.2%) in a water bath at 75℃, then mix it with 1.4 parts of persulfate (particle size 90 mesh), stir and cool on a magnetic stirrer (magnetic stirrer speed 150r / min, temperature 40℃) to obtain a mixture;

[0092] (2) After grinding and sieving the mixture (particle size of 50 mesh), add it to the granulator (adjust the disc angle to 40° and the temperature to 60°). When the disc speed reaches 15 r / min, add 1.3 parts of melted stearic acid for the first time to granulate and obtain a semi-finished product.

[0093] (3) Place the semi-finished product into a granulator (adjust the disc angle to 40° and the temperature to 60°), add 0.3 parts of melted stearic acid again for granulation, and obtain the granular persulfate slow-release material product with a particle size of 10 mm.

[0094] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A granular persulfate slow-release material, characterized by, The granular persulfate slow-release material has a core-shell structure; the core-shell structure comprises an outer shell and an inner core, wherein the outer shell is composed of stearic acid, and the inner core is composed of persulfate and stearic acid; The granular persulfate slow-release material comprises the following raw materials in parts by weight: 4.6-5.2 parts of stearic acid and 1-1.6 parts of persulfate; The particle size of the persulfate is 80-100 mesh; the type of the persulfate includes sodium persulfate and / or potassium persulfate; the melting point of the stearic acid is 67-70°C, and the amount of residual burning residue is ≤0.2%; The preparation method of the granular persulfate slow-release material comprises the following steps: (1) heating stearic acid to melt, then mixing with persulfate, stirring and cooling to obtain a mixture; (2) grinding and sieving the mixture, then adding to a granulator, when the rotation speed of the rotating disc reaches 15 r / min, adding melted stearic acid as a binder for granulation to obtain a semi-finished product; (3) putting the semi-finished product into the granulator, and granulating again by adding melted stearic acid to obtain the granular persulfate slow-release material; In step (1), the amount of stearic acid is 3.1-3.5 parts by weight, and the amount of persulfate is 1-1.6 parts by weight; In step (2), the amount of added melted stearic acid is 1.2-1.3 parts by weight; In step (3), the amount of added melted stearic acid is 0.3-0.4 parts by weight; In step (2), the particle size of the ground product is 40-60 mesh; In steps (2) and (3), the angle range of the granulator during granulation is 40-65°, and the temperature is 50-60°C.

2. The particulate persulfate slow-release material of claim 1, wherein, The release rate of persulfate in the granular persulfate slow-release material is 1-19 mg / (d·g); and the slow-release life of the granular persulfate slow-release material is 21-65 d.

3. A particulate persulfate slow-release material according to claim 2, wherein, The particle size of the granular persulfate slow-release material is 5-10 mm.

4. The particulate persulfate slow-release material of claim 1, wherein, In step (1), the heating process to melt is 75°C constant temperature water bath heating; the stirring temperature is 35-40°C, and the rotation speed is 100-150 r / min; and the cooling is natural cooling to room temperature.

5. The use of the granular persulfate slow-release material according to any one of claims 1-4 for in-situ chemical oxidation repair of groundwater.

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