Method for regenerating iron oxychloride adsorbents adsorbed with perfluorocarboxylic acids

Abstract

The invention relates to a method for regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid. The method comprises the following steps: 1) filtering and drying the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid; (2) adding 10 mg to 50 mg of dried iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid into 20 mL to 100 mL of persulfate aqueous solution with the concentration of 40 mg / L to 500 mg / L, and oscillating; 3) filtering the oscillated persulfate aqueous solution; and 4) drying the filtered matter to constant weight to obtain the regenerated iron oxychloride adsorbing.The regeneration method is low in energy consumption and environmentally friendly, the iron oxychloride adsorbent obtained through regeneration by the regeneration method still has high adsorption efficiency when being used for adsorbing perfluorocarboxylic acid compounds again, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to a method for regenerating an adsorbent, and particularly to a method for regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid. Background Art

[0002] With the rapid development of industry, perfluorocarboxylic acid compounds (PFCAs) are widely used in various industries and are widely present in media such as lakes, rivers, sewage and sediment in sewage treatment plants, which causes serious ecological damage and threatens human health. At present, using an iron oxychloride adsorbent to remove perfluorocarboxylic acid compounds in water by adsorption has become a promising method.

[0003] However, there are many deficiencies in the regeneration of the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid. For example, the reagent regeneration method mainly involves repeatedly washing the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid with saturated sodium chloride solution and methanol solution, but it is easy to produce high-salt wastewater and toxic wastewater, which is harmful to the environment and human health. The heating regeneration method requires high-temperature treatment of the iron oxychloride adsorbent (usually a high temperature greater than 300 °C), which consumes a large amount of energy and has a high cost; on the other hand, under high-temperature conditions, not only will the iron oxychloride decompose or undergo a phase change, such as being converted into α-Fe2O3 (hematite) or amorphous oxide, losing its original layered structure or active sites; but also the chlorine element will escape in the form of Cl2 or HCl, destroying the chemical composition of the material and resulting in a decrease in the adsorption capacity; high-temperature sintering will also cause particle agglomeration, reducing the porosity and specific surface area and affecting the subsequent adsorption performance.

[0004] Therefore, an improved method for regenerating the iron oxychloride adsorbent is needed. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of the claims.

[0006] In one aspect, the present application provides a method for regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid, the method comprising the following steps: 1) Filtering and drying the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid; 2) Adding 10 mg - 50 mg of the dried iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid to 20 mL - 100 mL of an aqueous persulfate solution with a concentration of 40 mg / L - 500 mg / L and oscillating; 3) Filtering the oscillated aqueous persulfate solution; and 4) Drying the filtrate to a constant weight to obtain the regenerated iron oxychloride adsorbent.

[0007] In one embodiment, the persulfate is selected from one or more of potassium peroxymonosulfate, potassium persulfate, and sodium persulfate.

[0008] In one embodiment, in step 2), the amount of perfluorocarboxylic acid adsorbed in the dried iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid is 7.5 mg - 10.6 mg.

[0009] In one embodiment, in step 1), the filtration is carried out using a filter membrane with a pore size of 0.22 μm - 0.45 μm.

[0010] In one embodiment, in step 2), the oscillation time is 20 min - 120 min, and the oscillation is carried out at a temperature of 20 - 30°C.

[0011] In one embodiment, in step 3), the filtration is carried out using a filter membrane with a pore size of 0.22 μm - 0.45 μm.

[0012] In one embodiment, in step 1), the perfluorocarboxylic acid is selected from one or more of perfluorobutyric acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorohexanoic acid, and perfluorodecanoic acid.

[0013] In one embodiment, in step 1), the iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid is obtained by the following method: at room temperature, 1 mg - 1500 mg of iron chloro-oxide is added to wastewater containing perfluorocarboxylic acid with a concentration of 0.1 mg / L - 150 mg / L, and the mixture is shaken for 0.5 - 24 hours to adsorb the perfluorocarboxylic acid in the wastewater onto the iron chloro-oxide adsorbent.

[0014] In one embodiment, the iron chloro-oxide adsorbent is obtained by dissolving FeCl3·6H2O in water, drying, then calcining, washing, and drying; alternatively, the iron chloro-oxide adsorbent is obtained by calcining, washing, and drying FeCl3·6H2O.

[0015] In the present application, the amounts represented by numerical ranges are not limited to the listed numerical values, and other unlisted numerical values or numerical ranges within the numerical range are equally applicable. For example, 10 mg - 50 mg of the iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid can represent the iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid such as 10 mg, 30 mg, etc., and can also represent the iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid in the ranges of 10 mg - 40 mg, 20 mg - 50 mg, etc.

[0016] On the other hand, the present application also provides the use of persulfate in regenerating the iron chloro-oxide adsorbent adsorbed with perfluorocarboxylic acid.

[0017] In this application, ferric oxychloride (FeOCl) is an efficient adsorbent that can adsorb perfluorocarboxylic acid compounds in water through surface coordination and electrostatic interactions. After adsorption saturation, the synergistic process of perfluorocarboxylic acid degradation and FeOCl regeneration is achieved by activating free radicals (SO4 - · / ·OH) with persulfate. The regeneration method of this application can protect the adsorption site structure of the adsorbent FeOCl while degrading pollutants through selective free radical attack and dynamic surface repair mechanisms.

[0018] Compared with the existing heating regeneration method, the regeneration method of the ferric oxychloride adsorbent provided in this application does not require high-temperature heating, does not generate huge energy consumption, and has a simple process and a short reaction time; compared with the existing reagent regeneration method, the regeneration method of the ferric oxychloride adsorbent provided in this application does not generate high-salt wastewater and toxic wastewater, and will not cause secondary pollution to the environment.

[0019] During the regeneration process of the regeneration method of this application, sulfate radicals are generated, which preferentially attack the adsorbed perfluorocarboxylic acid compounds rather than the ferric oxychloride adsorbent material itself, thereby reducing the structural damage of the ferric oxychloride adsorbent and maintaining its adsorption activity. The ferric oxychloride adsorbent regenerated by the regeneration method of this application still has a high adsorption efficiency when reused to adsorb perfluorocarboxylic acid compounds, and an extended service life is obtained.

[0020] The regeneration method of this application is applicable to the regeneration of ferric oxychloride adsorbents adsorbed with different types of perfluorocarboxylic acid compounds, and excellent regeneration effects can be obtained.

[0021] Other features and advantages of this application will be described in the subsequent specification, and part of them will become obvious from the specification or be understood by implementing this application. Other advantages of this application can be achieved and obtained through the solutions described in the specification. Brief Description of the Drawings

[0022] The drawings are used to provide an understanding of the technical solutions of this application, and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solutions of this application and do not constitute a limitation to the technical solutions of this application.

[0023] Figure 1A is the SEM photograph of the ferric oxychloride adsorbent adopted according to an embodiment of this application; Figure 1B is the SEM photograph of the ferric oxychloride adsorbent adopted according to another embodiment of this application. Detailed Description of the Embodiments

[0024] To make the objectives, technical solutions and advantages of this application clearer and more understandable, the embodiments of this application will be described in detail below. It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined arbitrarily with each other.

[0025] This application provides a method for regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid. The method includes the following steps: 1) filtering and drying the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid; 2) adding 10 mg - 50 mg of the dried iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid to 20 mL - 100 mL of an aqueous persulfate solution with a concentration of 40 mg / L - 500 mg / L and oscillating; 3) filtering the oscillated aqueous persulfate solution; and 4) drying the filtrate to a constant weight to obtain the regenerated iron oxychloride adsorbent.

[0026] In this application, the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid refers to the one obtained when the iron oxychloride adsorbent is used to adsorb perfluorocarboxylic acid compounds in water, especially in industrial wastewater.

[0027] In this application, industrial wastewater may refer to the wastewater discharged by factories during the production process. In addition to containing perfluorocarboxylic acid compounds, it may also contain other organic fluorides, some inorganic fluorides, heavy metals, etc., and usually has a pH in the range of 3 - 11.

[0028] In this application, the removal of perfluorocarboxylic acid compounds in water by the iron oxychloride adsorbent through adsorption can include an intermittent adsorption method and a dynamic adsorption method.

[0029] The intermittent adsorption method can include directly adding the iron oxychloride adsorbent to water containing perfluorocarboxylic acid compounds, performing constant-temperature oscillation and filtration to achieve the removal operation of perfluorocarboxylic acid compounds.

[0030] The dynamic adsorption method can include flowing water containing perfluorocarboxylic acid compounds through an adsorption column filled with the iron oxychloride adsorbent (fillers such as Al2O3 can also be provided on the column) to achieve the removal operation of perfluorocarboxylic acid compounds.

[0031] In this application, the iron oxychloride adsorbent can use commercially available iron oxychloride.

[0032] In this application, the iron oxychloride adsorbent can be prepared by the following method: Weigh 3.0 g of FeCl3·6H2O and dissolve it in 6 mL of water to prepare a precursor solution; dry the above precursor solution in an oven at 60°C for 12 h and calcine it in a muffle furnace at 250°C for 2.5 h; wash the calcined product with ultrapure water and acetone alternately for multiple times and dry it in an oven at 60°C to obtain the iron oxychloride adsorbent. Figure 1AThe SEM photograph of the prepared iron oxychloride adsorbent is shown, indicating that the iron oxychloride adsorbent is flower-shaped.

[0033] In addition, in the present application, the iron oxychloride adsorbent can be prepared by the following method: 3.0 g of FeCl3·6H2O is calcined in a muffle furnace at 250 °C for 2.5 h; the calcined product is washed alternately with ultrapure water and acetone for multiple times, and then dried in an oven at 60 °C to obtain the iron oxychloride adsorbent. Figure 1B The SEM photograph of the prepared iron oxychloride adsorbent is shown, indicating that the iron oxychloride adsorbent is rod-shaped.

[0034] The following examples specifically describe the method for regenerating the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid in the present application.

[0035] In the following examples, the materials used, unless otherwise specified, are all commercially available.

[0036] Example 1 Filter 50 mg of the iron oxychloride adsorbent (flower-shaped) adsorbed with 10.51 mg of perfluorooctanoic acid through a 0.22 μm MCE filter membrane, and then dry it to constant weight at 60 °C; At room temperature (25 °C), add the dried iron oxychloride adsorbent to 100 mL of an aqueous potassium persulfate solution with a concentration of 50 mg / L and shake for 60 min; after shaking, filter and dry to constant weight at 60 °C to complete the regeneration.

[0037] Example 2 Filter 50 mg of the iron oxychloride adsorbent (rod-shaped) adsorbed with 10.52 mg of perfluorononanoic acid through a 0.45 μm MCE filter membrane, and then dry it to constant weight at 60 °C; At room temperature (25 °C), add the dried iron oxychloride adsorbent to 100 mL of an aqueous sodium persulfate solution with a concentration of 300 mg / L and shake for 60 min; after shaking, filter and dry to constant weight at 60 °C to complete the regeneration.

[0038] Example 3 Filter 50 mg of the iron oxychloride adsorbent (rod-shaped) adsorbed with 10.50 mg of perfluorodecanoic acid through a 0.22 μm MCE filter membrane, and then dry it to constant weight at 60 °C; At room temperature (25 °C), add the dried iron oxychloride adsorbent to 100 mL of an aqueous potassium persulfate solution with a concentration of 400 mg / L and shake for 60 min; after shaking, filter and dry to constant weight at 60 °C to complete the regeneration.

[0039] Example 4 Filter 20 mg of the iron oxyhydroxide adsorbent (flower-shaped) adsorbed with 7.54 mg of perfluorobutyric acid using a 0.22 μm MCE filter membrane, and then dry it to a constant weight at 60°C; At room temperature (25°C), add the dried iron oxyhydroxide adsorbent to 100 mL of an aqueous potassium persulfate solution with a concentration of 500 mg / L and shake for 60 min; after shaking, filter and dry to a constant weight at 60°C to complete regeneration.

[0040] Determination of regeneration effect Redetermine the adsorption of the iron oxyhydroxide adsorbent obtained after regeneration in Examples 1 - 4. The adsorption is carried out in a batch adsorption mode. The adsorption process may include: at room temperature, add 50 mg of the iron oxyhydroxide adsorbent obtained after regeneration in Examples 1 - 4 to the wastewater containing 50 mg / L of perfluorocarboxylic acid and shake for 0.5 - 24 hours to adsorb the perfluorocarboxylic acid in the wastewater onto the iron oxyhydroxide adsorbent. Among them, the iron oxyhydroxide adsorbent obtained by regeneration in Example 1 is used to adsorb perfluorooctanoic acid, the iron oxyhydroxide adsorbent obtained by regeneration in Example 2 is used to adsorb perfluorononanoic acid, the iron oxyhydroxide adsorbent obtained by regeneration in Example 3 is used to adsorb perfluorodecanoic acid, and the iron oxyhydroxide adsorbent obtained by regeneration in Example 4 is used to adsorb perfluorobutyric acid. Repeat the above regeneration and adsorption processes a total of 5 times. After each regeneration and adsorption process is completed, the concentration of perfluorocarboxylic acid can be measured by methods such as liquid chromatography and tandem mass spectrometry (LC-MS-MS), and the adsorption rate of the iron oxyhydroxide adsorbent after regeneration to perfluorocarboxylic acid can be calculated. The adsorption rate calculation formula:

[0041] Among them, E is the adsorption rate, C0 is the initial concentration of perfluorocarboxylic acid before adsorption, and C t is the concentration of perfluorocarboxylic acid after adsorption. The results are shown in Table 1 below.

[0042] Table 1 Adsorption rate of the iron oxyhydroxide adsorbent after regeneration to perfluorocarboxylic acid (%)

[0043] It can be seen from the results in Table 1 that when the iron oxyhydroxide adsorbent regenerated in each example of the present application is reapplied to adsorb perfluorocarboxylic acid compounds in wastewater, even after 5 regenerations, the iron oxyhydroxide adsorbent still has a high adsorption rate for perfluorocarboxylic acid compounds.

[0044] Although not wishing to be bound by theory, it is believed that during the adsorption and regeneration processes of the present application, perfluorocarboxylic acid compounds hydrolyze in water and exist in the form of negative ions , the FeOCl material adsorbs perfluorocarboxylic acid compounds onto its surface through electrostatic adsorption; then, the generated radical SO4–· does not attack the perfluorocarboxylic acid compound skeleton due to its short half-life (30 μs) (the Fe-O bond energy in FeOCl is relatively high (~400 kJ / mol), tolerating the radical oxidation environment; the surface Cl⁻ can also reduce the direct attack of radicals on the Fe-O bond through electrostatic repulsion), but preferentially attacks the electron-rich region of perfluorocarboxylic acid, that is, the carboxylic acid group, triggering decarboxylation and chain scission, destroying the association between the perfluorocarboxylic acid compound and the adsorption site, and releasing the adsorption site; ·OH (with a half-life of 1 ns) non-selectively attacks the C-F bond, promoting defluorination reactions. On the other hand, perfluorocarboxylic acid molecules prevent radicals from entering the interior of the adsorbent material, confining the reaction to the material surface and avoiding damage to the bulk structure; at the same time, radical oxidation dissolves the organic coating layer formed on the FeOCl surface due to the adsorption of perfluorocarboxylic acid, exposing fresh active sites and restoring the adsorption capacity.

[0045] In addition, for the iron oxychloride adsorbent used in this application, its Fe-O-Cl structure can also achieve dynamic repair, including Fe 2 + / Fe 3+ cycle promotes the regeneration of surface oxygen vacancies and maintains the stability of the layered structure of FeOCl; Fe in FeOCl 3+ is reduced to Fe 2+ when reacting with, for example, PMS, and at the same time, oxygen vacancies (V0) are generated; under oxidation conditions, Fe 2+ is re-oxidized to Fe 3+ , the oxygen vacancies are filled, and the adsorption capacity is restored; the oxygen vacancies, as electron defects, balance the charge fluctuations caused by the valence change of Fe 2+ / Fe 3+ to prevent lattice distortion caused by local charge accumulation; the electron localization effect around the oxygen vacancies enhances the electrostatic interaction between the FeOCl layers and improves the overall structural stability.

[0046] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A method for regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid, characterized in that, The method includes the following steps: 1) Filter and dry the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid; 2) Add 10 mg - 50 mg of the dried iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid to 20 mL - 100 mL of an aqueous persulfate solution with a concentration of 40 mg / L - 500 mg / L and shake; 3) Filter the shaken aqueous persulfate solution; and 4) Dry the filtrate to a constant weight to obtain the regenerated iron oxychloride adsorbent.

2. The method according to claim 1, wherein The persulfate is selected from one or more of potassium peroxymonosulfate, potassium persulfate, and sodium persulfate.

3. The method according to claim 1, wherein In step 2), the amount of perfluorocarboxylic acid adsorbed in the dried iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid is 7.5 mg - 10.6 mg.

4. The method according to claim 1, wherein In step 1), the filtration is carried out using a filter membrane with a pore size of 0.22 μm - 0.45 μm.

5. The method according to claim 1, characterized in that, In step 2), the shaking time is 20 min - 120 min, and the shaking is carried out at a temperature of 20 - 30°C.

6. The method according to claim 1, characterized in that, In step 3), the filtration is carried out using a filter membrane with a pore size of 0.22 μm - 0.45 μm.

7. The method according to any one of claims 1-6, characterized in that, In step 1), the perfluorocarboxylic acid is selected from one or more of perfluorobutyric acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorohexanoic acid, and perfluorodecanoic acid.

8. The method according to any one of claims 1-6, characterized in that, In step 1), the iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid is obtained by the following method: at room temperature, add 1 mg - 1500 mg of iron oxychloride to wastewater containing perfluorocarboxylic acid with a concentration of 0.1 mg / L - 150 mg / L, and shake for 0.5 - 24 hours to adsorb the perfluorocarboxylic acid in the wastewater onto the iron oxychloride adsorbent.

9. The method according to any one of claims 1-6, characterized in that, The iron oxychloride adsorbent is obtained by dissolving FeCl3·6H2O in water, drying, then calcining, washing, and drying; or, the iron oxychloride adsorbent is obtained by calcining, washing, and drying FeCl3·6H2O.

10. Use of persulfate in regenerating an iron oxychloride adsorbent adsorbed with perfluorocarboxylic acid.

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