Reinforced heterogeneous Fenton water treatment method based on iron modified montmorillonite

Abstract

The invention discloses a reinforced heterogeneous Fenton water treatment method based on iron-modified montmorillonite, and relates to the technical field of water treatment.The method comprises the steps that firstly, a FeCl3 solution is used for conducting ion exchange treatment on montmorillonite to obtain iron-modified montmorillonite (Fe-MMT), an activating agent and H2O2 are added, a Fe-MMT / activating agent / H2O2 heterogeneous Fenton reaction system is constructed, and the Fe-MMT / activating agent / H2O2 heterogeneous Fenton reaction system is prepared; the method has the advantages of high treatment efficiency, environment friendliness and the like, and can generate economic benefits and social benefits in the field of treatment of organic wastewater such as printing and dyeing wastewater and antibiotic wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to an enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite. Background Art

[0002] The problem of water pollution has become a huge challenge faced by mankind all over the world. Organic pollutants are ubiquitous in the water environment. Common types such as dyes and antibiotics pose a potential threat to the ecological environment and human health and safety. Studies have found that the Fenton-like system formed by fixing iron salts on porous materials can effectively solve the problem of difficult recycling of catalysts, and can also expand the pH range of the reaction. Due to the large specific surface area of ​​porous materials, they can not only solidify iron, but also adsorb and enrich organic matter to accelerate the reaction process. Therefore, for heterogeneous Fenton-like catalytic reactions, it is crucial to find a suitable porous material.

[0003] Montmorillonite is a 2:1 layered silicate clay mineral composed of two layers of silicon-oxygen tetrahedrons with a layer of aluminum-oxygen octahedron sandwiched between them. It has the characteristics of large specific surface area, high expansion performance, and strong cation exchange capacity. It is a natural material with porosity and excellent chemical and physical properties. It has abundant reserves in my country and is inexpensive. Studies have shown that montmorillonite saturated with variable-valence transition metals can improve the catalytic performance of montmorillonite, making it better at catalytically degrading organic pollutants. Fe-montmorillonite (Fe-MMT) is a typical representative of them, with the advantages of a wide range of applications and high reaction activity. Using it as an iron source and catalyst in a Fenton-like reaction system can effectively solve the problem of iron mud and increase the pH adaptability range of the reaction. Summary of the invention

[0004] The object of the present invention is to provide an enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: an enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite, wherein montmorillonite is subjected to ion exchange treatment using a FeCl3 solution to obtain iron-modified montmorillonite Fe-MMT, and Fe-MMT, an activator, and H2O2 are added to construct a Fe-MMT / activator / H2O2 heterogeneous Fenton reaction system to remove organic pollutants.

[0006] A method for preparing iron-modified montmorillonite comprises the following steps:

[0007] S1. Dispersing montmorillonite in pure water to obtain a montmorillonite suspension, and adjusting its pH to 6.8, and stabilizing it for at least 8 hours to remove carbonate impurities in the mineral;

[0008] S2. The suspension was centrifuged at 600 rpm for 15 min, and the precipitate was removed to remove particles with a diameter ≥ 2 μm in the suspension;

[0009] S3. The montmorillonite suspension obtained in step S2 is added with iron salt to perform cation exchange, and after vigorous stirring for 8 hours, high-speed centrifugation is performed at >8000rpm to collect the precipitate;

[0010] S4. The montmorillonite saturated with iron salt was repeatedly washed with ultrapure water until no precipitation was produced by adding AgNO3 to the supernatant after centrifugation;

[0011] S5. The washed montmorillonite is freeze-dried, ground using an agate mortar, passed through a 100-mesh sieve, and stored dry.

[0012] Preferably, the montmorillonite is calcium montmorillonite and / or sodium montmorillonite;

[0013] The amount of the montmorillonite is 400-1000 g, and the concentration of the montmorillonite suspension is 1 g / L;

[0014] The iron salt includes iron sulfate and / or iron chloride;

[0015] The amount of iron salt added is such that its final concentration is 0.1-0.15 mol / L;

[0016] The cation exchange is repeated 2-6 times, each time lasting 6-12 hours.

[0017] Preferably, after the reaction in step S3, the mixed solution is centrifuged and washed with deionized water three times, and finally the catalyst is placed in a 60° C. forced air drying oven to dry and recover the catalyst.

[0018] Preferably, the dosage of Fe-MMT is 0.5-2 g / L.

[0019] Preferably, the types of activators include hydroxylamine hydrochloride, ascorbic acid, polyphenols, etc., and the dosage is 0.5-2mmol / L.

[0020] Preferably, the H2O2 dosage is 1-4 mmol / L.

[0021] Preferably, the organic pollutants include methyl orange, rhodamine B, tetracycline, dimethyl phthalate, bisphenol A, etc., and the initial concentration is 0 to 100 mg / L, and is not 0.

[0022] Preferably, in step S1, hydrochloric acid and sodium hydroxide are used to adjust the acidity and alkalinity of the solution.

[0023] Preferably, the mixing of the catalyst and the wastewater is achieved by stirring.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention provides a Fenton-like water treatment method based on the generation of hydroxyl radicals by iron-containing clay minerals, using cheap iron salt saturated montmorillonite to prepare Fe-MMT, promoting the degradation of pollutants by adding an activator, constructing a Fe-MMT / activator / H2O2 reaction system, and then degrading organic pollutants in water and adsorbed on the surface of Fe-MMT. The method has the advantages of high treatment efficiency and environmental friendliness, and can generate economic and social benefits in the field of treatment of organic wastewater such as printing and dyeing wastewater and antibiotic wastewater;

[0026] 2. Clay minerals are cheap and widely available. The iron salt saturation method has the characteristics of mild preparation conditions and no secondary pollution;

[0027] 3. In the process of water treatment, under the mediation of the activator, the iron circulation is promoted. During the reaction, very little iron ion is dissolved, and a large amount of iron sludge will not be produced, thus reducing the cost of sludge treatment and disposal;

[0028] 4. In the present invention, when the pH is weakly acidic (5-6), the removal rate of organic pollutants can be maintained at more than 75%;

[0029] 5. In the present invention, by adding an activator, the amount of H2O2 added is greatly reduced compared to the ordinary Fenton reaction, saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The enhancement effect of adding the activator HA in Example 1 of the present invention

[0031] Figure 2 is the degradation rate of different organic matter by the Fe-MMT / H2O2 / HA system in Example 2 of the present invention;

[0032] Figure 3 is the removal rate of MO by the Fe-MMT / H2O2 / HA system at different pH values ​​in Example 3 of the present invention;

[0033] Figure 4 The Fe-MMT / H2O2 / HA system clay surface and supernatant in Example 4 of the present invention is 2+ Content;

[0034] Figure 5 is the removal rate of MO in the Fe-MMT / H2O2 / HA system in Example 5 of the present invention after 5 times of Fe-MMT reuse;

[0035] Figure 6 This is the electron paramagnetic resonance spectrum of the reaction system of Example 6 of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Embodiment 1;

[0038] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite in 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1M FeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely FeCl3-free. 3+ (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01M AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0039] Step 2: Under magnetic stirring at 25±2℃, add 50mg / L MO solution to a 100mL conical flask, and add a certain amount of HA, H2O2, Fe-MMT, H2O2, HA, H2O2+HA, Fe-MMT+HA, Fe-MMT+H2O2, Fe-MMT+HA+H2O2, respectively. Stir the reaction for 30 minutes and take samples. Add the 2mL sample taken out to the sampling tube to which 2mL methanol has been added, and mix the sample evenly to end the reaction. Centrifuge the sample taken out at 8000rpm in a high-speed centrifuge, take the supernatant, and then filter it with a 0.22μm filter membrane and measure the absorbance of the solution.

[0040] The removal rates of MO in HA, H2O2, Fe-MMT, HA+H2O2, Fe-MMT+HA, Fe-MMT+H2O2, and Fe-MMT+H2O2+HA systems were 2%, 15%, 36%, 15%, 41%, and 97%, respectively, which strongly proved that the addition of activator HA was beneficial to the degradation and removal of methyl orange. Figure 1 .

[0041] Embodiment 2;

[0042] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite in 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1M FeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely FeCl3-free. 3+ saturated; (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01 mol / L AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0043] Step 2: Under magnetic stirring conditions, add a certain concentration of methyl orange (MO), rhodamine B (RhB), tetracycline (TC), dimethyl phthalate (DMP), bisphenol A (BPA) to a 100mL conical flask, add a certain amount of Fe-MMT, HA and H2O2, stir and react for 30 minutes and take a sample. Add the 2mL sample taken out to the sampling tube to which 2mL of methanol has been added, and mix the sample evenly to end the reaction. The sample taken out is centrifuged at 8000rpm in a high-speed centrifuge, and the supernatant is taken, and then filtered with a 0.22μm filter membrane and the absorbance of the solution is measured.

[0044] The removal rates of MO, RhB, TC, DMP and BPA by Fe-MMT+H2O2+HA system were all higher than 95%, indicating that the system provided by the present invention can degrade a variety of refractory organic pollutants and has good application prospects in the field of organic wastewater treatment. Figure 2 .

[0045] Embodiment 3;

[0046] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite in 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1M FeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely FeCl3-free. 3+ saturated; (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01 mol / L AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0047] Step 2: Under magnetic stirring conditions, add a certain concentration of MO solution and catalyst to a 100 mL conical flask, so that the MO concentration is 20 mg / L and the Fe-MMT concentration is 0.5 g / L, and adjust the pH value to 3, 4, 5, and 6 with 0.1 mol / L HCl solution and NaOH solution;

[0048] Step 3: In step 2, add H2O2 and HA at 4 and 2 mmol / L respectively, stir and react for 30 minutes and take samples. Add 2 mL of sample taken out to the sampling tube with 2 mL of methanol, mix the sample evenly to end the reaction. Centrifuge the sample taken out at 8000 rpm in a high-speed centrifuge, take the supernatant, filter it with a 0.22 μm filter membrane, and measure the absorbance of the solution.

[0049] In the Fe-MMT / HA / H2O2 system of the present invention, when the pH is weakly acidic (5-6), the removal rate of MO can be maintained above 75%. Figure 3 .

[0050] Embodiment 4;

[0051] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite in 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1M FeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely FeCl3-free. 3+ saturated; (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01 mol / L AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0052] Step 2: Under magnetic stirring conditions, add a certain concentration of MO solution and catalyst into a 100 mL conical flask, so that the MO concentration is 20 mg / L and the Fe-MMT concentration is 0.5 g / L, and adjust the pH value to 4 with 0.1 mol / L HCl solution and NaOH solution;

[0053] Step 3: Samples were taken at different time periods between 0 and 300 min, and the Fe 2+ The results showed that after MO reacted in the Fe-MMT / HA / H2O2 system for 300 minutes, the solution had almost no Fe 2+ , Fe on the Fe-MMT surface 2+ The content increased from the initial 3.4 mg·L -1 Increased to 12.0 mg·L -1 , indicating that the Fe2+ generated in the reaction system is mainly adsorbed on the mineral surface, see Figure 4 In short, Fe-MMT does not produce a large amount of iron sludge like the traditional Fenton reaction.

[0054] Embodiment 5;

[0055] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite into 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1mol / LFeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely Fe 3+ saturated; (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01 mol / L AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0056] Step 2: Under magnetic stirring conditions, add a certain concentration of MO solution and catalyst to a 100 mL conical flask, so that the MO concentration is 20 mg / L, the Fe-MMT concentration is 0.5 g / L, the HA dosage is 2 mmol / L, the H2O2 dosage is 4 mmol / L, and the pH value is adjusted to 4 with 0.1 mol / L HCl solution and NaOH solution;

[0057] Step 3: After each reaction, centrifuge at 8000 rpm using a high-speed centrifuge, wash with deionized water three times, recover the catalyst, and finally dry the catalyst in a 60°C forced air drying oven for the next experiment. Repeat the above experimental process four times to investigate the reusability of Fe-MMT.

[0058] Fe-MMT was recycled for 5 times, and the removal rate of MO did not change significantly, which was higher than 96%, indicating that Fe-MMT catalyst can be recycled for many times and its catalytic activity is very stable. Figure 5 .

[0059] Embodiment 6;

[0060] Step 1: The specific steps of the catalyst preparation process are as follows: (1) Use a stirrer to evenly disperse 400g of montmorillonite in 4.0L of pure water; (2) Use 0.5M acetic acid-sodium acetate buffer (pH=5.0) to adjust the pH of the suspension to 6.8 and keep it stable for 8h. The purpose of this step is to remove carbonate impurities in the montmorillonite mineral; (3) Centrifuge the suspension at 600rpm for 15min and remove the supernatant. The purpose of this step is to remove particles with a diameter of ≥2μm in the suspension; (4) Resuspend the montmorillonite obtained by precipitation in ultrapure water and add 0.1M FeCl3 solution to perform ion exchange treatment. After vigorous stirring for 8h, centrifuge at 5000rpm for 15min; (5) Repeat the above steps 3 times to ensure that the exchangeable cation sites between the montmorillonite layers are completely FeCl3-free. 3+ saturated; (6) repeatedly washing the saturated montmorillonite with ultrapure water until no precipitation is produced after adding 0.01 mol / L AgNO3 to the supernatant after centrifugation; (7) freeze-drying the saturated montmorillonite, grinding it with an agate mortar, passing it through a 100-mesh sieve, and storing it in a dry place.

[0061] Step 2: Under magnetic stirring conditions, Fe-MMT, HA and H2O2 were mixed to a concentration of 0.5 g / L, 2 mmmol / L and 4 mmol / L, respectively. 1 mL of the mixture was added with DMPO to a final concentration of about 100 mmol / L. The mixture was shaken for 10 to 20 times, and the spectrum of the free radical adducts produced in the system was determined using EPR technology. A similar operation was performed on the control group.

[0062] DMPO, H2O2, and HA did not generate any signal, while the signals generated by Fe-MMT and Fe-MMT / H2O2 were very weak. The EPR of the Fe-MMT / HA / H2O2 system showed four significant split peaks with intensities of 1:2:2:1, which were ·OH. ·OH is the active oxygen in this reaction system, with a standard reduction potential of up to 2.8V, and can oxidize various organic pollutants at a rate close to diffusion control. For details, see Figure 6 .

[0063] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. An enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite, characterized in that: Montmorillonite was treated with ion exchange using FeCl3 solution to obtain iron-modified montmorillonite Fe-MMT. Fe-MMT, activator and H2O2 were added to construct a Fe-MMT / activator / H2O2 heterogeneous Fenton reaction system to remove organic pollutants.

2. The method for preparing the iron-modified montmorillonite according to claim 1, characterized in that: The following steps are involved: S1. Dispersing montmorillonite in pure water to obtain a montmorillonite suspension, and adjusting its pH to 6.8, and stabilizing it for at least 8 hours to remove carbonate impurities in the mineral; S2. The suspension was centrifuged at 600 rpm for 15 min, and the precipitate was removed to remove particles with a diameter ≥ 2 μm in the suspension; S3. The montmorillonite suspension obtained in step S2 is added with iron salt to perform cation exchange, and after vigorous stirring for 8 hours, high-speed centrifugation is performed at >8000rpm to collect the precipitate; S4. The montmorillonite saturated with iron salt was repeatedly washed with ultrapure water until no precipitation was produced by adding AgNO3 to the supernatant after centrifugation; S5. The washed montmorillonite is freeze-dried, ground using an agate mortar, passed through a 100-mesh sieve, and stored dry.

3. The method for preparing an iron-modified montmorillonite according to claim 2, characterized in that: The montmorillonite is calcium montmorillonite and / or sodium montmorillonite; The amount of the montmorillonite is 400-1000 g, and the concentration of the montmorillonite suspension is 1 g / L; The iron salt includes iron sulfate and / or iron chloride; The amount of iron salt added is such that its final concentration is 0.1-0.15 mol / L; The cation exchange is repeated 2-6 times, each time lasting 6-12 hours.

4. The method for preparing an iron-modified montmorillonite according to claim 2, characterized in that: After the reaction in step S3, the mixed solution is centrifuged and washed with deionized water three times. Finally, the catalyst is placed in a forced air drying oven at 60° C. to dry and recover the catalyst.

5. The enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite according to claim 1, characterized in that: The dosage of Fe-MMT is 0.5-2g / L.

6. The enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite according to claim 1, characterized in that: The types of activators include hydroxylamine hydrochloride, ascorbic acid, polyphenols, etc., and the dosage is 0.5-2mmol / L.

7. The enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite according to claim 1, characterized in that: The H2O2 dosage is 1-4 mmol / L.

8. The enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite according to claim 1, characterized in that: The organic pollutants include methyl orange, rhodamine B, tetracycline, dimethyl phthalate, bisphenol A, etc., and the initial concentration is 0 to 100 mg / L and is not 0.

9. The method for preparing an iron-modified montmorillonite according to claim 2, characterized in that: In step S1, hydrochloric acid and sodium hydroxide are used to adjust the acidity and alkalinity of the solution.

10. The enhanced heterogeneous Fenton water treatment method based on iron-modified montmorillonite according to claim 1, characterized in that: The catalyst and wastewater are mixed by stirring.

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