Amine-modified ferroferric oxide for removing phosphorus from wastewater as well as preparation method and application of amine-modified ferroferric oxide

Abstract

The invention belongs to the technical field of water treatment adsorption, and discloses amine-modified ferroferric oxide for wastewater phosphorus removal and a preparation method and application thereof.The preparation method comprises the following steps that ferric acetylacetonate and long-chain organic amine are dissolved in absolute ethyl alcohol, and a dark red clear solution is obtained; performing constant-temperature water bath on 1-octadecene for later use; under the condition of stirring, slowly dropwise adding the dark red clear solution into the 1-octadecene, and continuously performing constant-temperature water bath to obtain a mixed solution; transferring the mixed solution into a reaction kettle, and carrying out high-temperature reaction in an inert atmosphere to obtain a black mixture; and sequentially carrying out magnetic separation, washing and freeze drying on the black mixture to obtain the amine modified ferroferric oxide. The prepared amine-modified ferroferric oxide has the advantages of strong saturation magnetization, rapid and deep phosphorus removal capability, high phosphate selectivity, environment friendliness and the like, and the adsorption capacity of the amine-modified ferroferric oxide is more than two times that of an unmodified material.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment adsorption, and particularly relates to an amine-modified iron oxide and its preparation method and application for phosphorus removal from wastewater. Background Art

[0002] At present, phosphorus pollution in water bodies is still serious, and China's phosphorus discharge standards are becoming more stringent. The demand for deep phosphorus removal from sewage with low phosphorus concentration is constantly expanding. At present, the commonly used sewage phosphorus removal methods mainly include biological method, chemical precipitation method, membrane separation method, adsorption method, etc. The adsorption method has been widely used in the treatment of phosphorus-containing sewage due to its advantages of simple operation, low cost, recyclability, etc.

[0003] The key to the effect of the adsorption method lies in the adsorption material. Among many adsorption materials, metal-based materials have received more and more attention due to their excellent adsorption ability and high phosphate affinity. For example, metals such as aluminum, calcium, cerium, magnesium, zinc, and zirconium are widely used in the preparation of phosphorus removal materials and have achieved good application effects. However, in practical applications, such materials still have obvious deficiencies: (1) The synthesis cost is too high to enable large-scale production; (2) The recovery process is cumbersome and the loss during use is large; (3) The compounding method is complex, introducing secondary pollution and making it difficult to evaluate the environmental risks.

[0004] Due to its cost-effectiveness and environmental compatibility, iron-based materials are more promising for actual sewage treatment in the future compared with other metals. In particular, iron oxide materials provide an excellent solution for the recovery and regeneration of adsorbents due to their prominent magnetic characteristics. However, compared with rare earth metals such as lanthanum and zirconium, iron oxide has a lower affinity for phosphates, resulting in a relatively slow adsorption kinetics. In actual phosphorus removal applications, higher requirements are often placed on the adsorption rate, adsorption selectivity, and adsorption capacity, especially for the treatment of sewage with low phosphorus concentration. Based on this background, this application proposes to enhance the phosphorus removal performance of iron oxide through modification means in order to achieve rapid selective phosphorus removal and efficient recovery in phosphorus-containing wastewater. However, the method of doping high-affinity metals will increase the material preparation cost; the method of preparing core-shell structure adsorbents with iron oxide as the core will shield the active sites on the iron oxide, affecting the phosphorus removal performance and magnetism of the adsorption material. In view of this, it is very necessary to apply a more suitable modification means to obtain iron oxide nanomaterials that can adsorb and remove phosphorus quickly and selectively with high selectivity. Summary of the Invention

[0005] In view of the above deficiencies existing currently, the present invention provides an amine-modified iron oxide and its preparation method and application for phosphorus removal from wastewater. The amine-modified iron oxide prepared in this application has the advantages of strong saturation magnetization intensity, rapid and deep phosphorus removal ability, high phosphate selectivity, an adsorption capacity more than twice that of the unmodified material, and environmental friendliness.

[0006] To achieve the above object, the present invention provides a method for preparing amine-modified iron tetroxide, comprising the following steps:

[0007] S1. Dissolve iron acetylacetonate and long-chain organic amine in absolute ethanol to obtain a dark red clear solution; subject 1-octadecene to a constant temperature water bath for later use;

[0008] S2. Under stirring, slowly drop the dark red clear solution into the 1-octadecene and continue the constant temperature water bath to obtain a mixed solution;

[0009] S3. Transfer the mixed solution into a reaction kettle and, after high-temperature reaction in an inert atmosphere, obtain a black mixture;

[0010] S4. Subject the black mixture to magnetic separation, washing, and freeze-drying in sequence to obtain amine-modified iron tetroxide.

[0011] According to one aspect of the present invention, in step S1, the long-chain organic amine includes at least one of octadecylamine, N-methyloctadecylamine, and N,N-dimethyloctadecylamine.

[0012] According to one aspect of the present invention, in step S1, the molar ratio of iron acetylacetonate to long-chain organic amine is 1:0.5 to 3.

[0013] According to one aspect of the present invention, in step S2, the volume ratio of 1-octadecene to the dark red clear solution is 1:0.1 to 0.4.

[0014] According to one aspect of the present invention, in step S2, the temperature of the constant temperature water bath is 75 to 100 °C, and the time is 1 to 2 h; the rate of slow dropping is 1 to 5 mL / min.

[0015] According to one aspect of the present invention, in step S3, the temperature of the high-temperature reaction is 160 to 220 °C, and the time is 5 to 24 h.

[0016] According to one aspect of the present invention, in step S3, the inert atmosphere is at least one of nitrogen and argon.

[0017] According to one aspect of the present invention, in step S3, the washing is to wash successively with an organic detergent and deionized water multiple times respectively; the detergent includes absolute ethanol and hexane; the time of freeze-drying is 6 to 24 h.

[0018] Based on the same inventive concept, the present invention also provides an amine-modified iron tetroxide prepared by any of the above preparation methods.

[0019] Based on the same inventive concept, the present invention also provides an application of the above amine-modified magnetite in the deep adsorption and phosphorus removal from sewage.

[0020] Advantages of the present invention:

[0021] (1) The present invention provides a preparation method of an amine-modified magnetite adsorption material. Using anhydrous ethanol as a co-solvent, it promotes the dissolution of iron acetylacetonate into 1-octadecene (solvent, reducing agent). The decomposition, reduction of iron acetylacetonate, and the nucleation of magnetite and grafting of organic amine are completed through a one-step high-temperature reaction. The whole preparation process is simple and controllable. The main raw materials for synthesis are common reaction reagents, with high economy, good environmental protection, and low pollution risk. The synthesized product is of nanoscale size and has a large specific surface area, which is beneficial for adsorption.

[0022] (2) The isoelectric point of magnetite is generally in the acidic pH range, while the pH of municipal sewage is often neutral. Therefore, in sewage treatment applications, the surface of magnetite will carry a negative charge, which is not conducive to the adsorption of negatively charged phosphate. The present invention grafts organic amine on the surface of magnetite through the iron-nitrogen coordination mechanism, improving the isoelectric point and making the modified material carry a positive charge on the surface under neutral conditions. At the same time, the long carbon chain of the organic amine extends from the surface of magnetite into the water, which can increase the degree of collision with phosphate molecules and is beneficial to accelerating adsorption.

[0023] (3) The amine-modified magnetite material of the present invention has a fast adsorption rate. The adsorption equilibrium time is shortened by more than 2 times compared with the pure magnetite material, and the removal rate of low-concentration phosphorus is higher than 95%. In addition, it can be quickly magnetically recovered with low application loss. This material is suitable for deep phosphorus removal at the end of sewage treatment. Description of the drawings

[0024] Figure 1 XRD patterns of the products of Example 1 and Comparative Examples 1-2 of the present invention;

[0025] Figure 2 SEM images of the products of Example 1 and Comparative Examples 1-2 of the present invention; among them, (a) is Sample 1 of Example 1; (b) is Sample 2 of Comparative Example 1; (c) is Sample 3 of Comparative Example 2;

[0026] Figure 3 TEM image and EDS energy spectrum of Sample 1 of Example 1 of the present invention; (a) is the TEM image of Sample 1; (b) is the element distribution map of Sample 1; (c) is the Fe element distribution map of Sample 1; (d) is the O element distribution map of Sample 1; (e) is the N element distribution map of Sample 1;

[0027] Figure 4 Hysteresis curve of Sample 1 of Example 1 of the present invention;

[0028] Figure 5 The deep adsorption and phosphorus removal effect diagrams of the products of Example 1 and Comparative Example 1 of the present invention;

[0029] Figure 6 The adsorption effect diagrams of phosphorus by the products of Example 1 and Comparative Example 1 of the present invention under the coexistence conditions of other interfering anions;

[0030] Figure 7 The fitting curves of the isothermal adsorption equations of the products of Example 1 and Comparative Example 1 of the present invention;

[0031] Figure 8 The substance leaching diagrams of the products of Example 1 and Comparative Examples 1-2 of the present invention. Specific embodiments

[0032] To make the present invention easier to understand, the present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below have the same meaning as understood by those of ordinary skill in the art; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by well-known methods.

[0033] It should be noted that long-chain organic amines are professional terms referring to organic amines with more than 10 carbon atoms.

[0034] Example 1

[0035] A preparation method of amine-modified magnetite, comprising the following steps:

[0036] (1) Take 0.353 g of iron acetylacetonate and add it to 15 mL of absolute ethanol, ultrasonically dissolve for 30 min, then weigh 0.269 g of octadecylamine and add it thereto, ultrasonically dissolve for 30 min to obtain a clear solution; measure 50 mL of 1-octadecene and put it into a beaker, heat it in a water bath to 75 °C and keep it constant.

[0037] (2) Slowly drop the above-mentioned clear solution (3 mL / min) into 1-octadecene with a plastic dropper, and shake it evenly while dropping. Keep the water bath for 1 h to completely volatilize the ethanol to obtain a clear mixed solution.

[0038] (3) Transfer the clear mixed solution in the beaker to a stainless steel reaction kettle, pass nitrogen into the reaction kettle for 5 min, quickly tighten the lid, screw on the outer cover of the reaction kettle, put it into an oven, and maintain it at 180 °C for 12 h to obtain a black mixture.

[0039] (4) After the reaction kettle is cooled, the black solid-liquid mixture inside is magnetically separated with a magnet. After being washed repeatedly with n-hexane, ethanol, and deionized water, the solid is freeze-dried to obtain amine-modified iron oxide (Sample 1).

[0040] Comparative Example 1

[0041] A preparation method of iron oxide, comprising the following steps:

[0042] (1) Weigh 0.353 g of iron acetylacetonate and add it to 15 mL of absolute ethanol. Ultrasonic for 30 min to dissolve and obtain a clear solution. Measure 50 mL of 1-octadecene and put it into a beaker, heat it in a water bath to 75 °C and keep it constant.

[0043] (2) Slowly drip the above clear solution (3 mL / min) into 1-octadecene with a plastic dropper, and shake evenly while dripping. Keep the water bath for 1 h to completely volatilize the ethanol and obtain a clear mixed solution.

[0044] (3) Transfer the clear mixed solution in the beaker to a stainless steel reaction kettle. After introducing nitrogen into the reaction kettle for 5 min, quickly tighten the lid, screw on the outer cover of the reaction kettle, and put it into an oven. Maintain it at 180 °C for 12 h to obtain a black mixture.

[0045] (4) After the reaction kettle is cooled, the black solid-liquid mixture inside is magnetically separated with a magnet. After being washed repeatedly with n-hexane, ethanol, and deionized water, the solid is freeze-dried to obtain iron oxide (Sample 2).

[0046] Comparative Example 2

[0047] Commercially available nano-scale iron oxide (Sample 3) purchased.

[0048] Performance detection and result analysis:

[0049] The products of Example 1 and Comparative Examples 1-2 were respectively subjected to X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) analysis, and the results are as Figures 1 to 3 shown. It can be Figure 1 seen that the products synthesized in Example 1 and Comparative Example 1 of this application are both iron oxide. It can be Figure 2 seen that the morphologies of the products prepared in Example 1 and Comparative Example 1 are similar, both presenting a block formed by the accumulation of small particles; while the product of Comparative Example 2 presents a small ball cluster shape. The product of Example 1 was subjected to transmission electron microscopy (TEM) and vibrating sample magnetometer analysis, and the results are as Figures 3 to 4 shown. It can be Figure 3It can be seen that the product prepared in Example 1 consists of irregular nanocrystals. Its EDS spectrum shows that there are a large number of Fe, O, and N elements on the material, and the presence of N element indicates that the surface organic amine has been successfully grafted onto the material. From Figure 4 the hysteresis curve, it can be seen that Sample 1 of Example 1 is paramagnetic and has a strong saturation magnetization intensity. A magnet can separate Sample 1 from the aqueous solution within 1 minute.

[0050] Prepare a low-concentration potassium dihydrogen phosphate solution with a phosphorus concentration of 2 mg / L. According to the dosage ratio of 1 g adsorbent per 1 L potassium dihydrogen phosphate solution, add Sample 1 in Example 1 and Sample 2 in Comparative Example 1 to the potassium dihydrogen phosphate solution respectively, and carry out the adsorption reaction at a temperature of 25 °C and a rotation speed of 180 rpm. At 0, 2, 5, 10, 30, 60, and 120 minutes, use a disposable syringe to take the supernatant, filter it through a 0.45 μm aqueous filter membrane, and measure the phosphorus concentration by the ammonium molybdate spectrophotometric method. The results are as Figure 5 shown. From Figure 5 it can be seen that Sample 1 in Example 1 of this application removed nearly 90% of the phosphate at 2 minutes of adsorption. After 10 minutes of adsorption, the phosphorus concentration dropped to about 0.1 mg / L, and then basically tended to reach the adsorption equilibrium; while Sample 2 in Comparative Example 1 only removed 40% of the phosphate at 2 minutes of adsorption, and at 120 minutes of adsorption, the phosphorus concentration was still at the level of 0.5 mg / L. This shows that the amine-modified iron oxide (Sample 1) can quickly capture phosphorus from water, and the removal rate is much higher than that of the unmodified iron oxide (Sample 2). The modification strategy is very successful, indicating that Sample 1 in Example 1 of this application has the ability to quickly and deeply remove phosphorus.

[0051] Prepare an aqueous solution with a phosphorus concentration of 2 mg / L and 100 mg / L of each of the three interfering ions, sulfate, chloride, and nitrate. According to the dosage ratio of 1 g adsorbent per 1 L aqueous solution, add Sample 1 in Example 1 and Sample 2 in Comparative Example 1 to the aqueous solution respectively, and carry out the adsorption reaction at a temperature of 25 °C and a rotation speed of 180 rpm. At 0, 2, 5, 10, 30, 60, and 120 minutes, use a disposable syringe to take the supernatant, filter it through a 0.45 μm aqueous filter membrane, and measure the phosphorus concentration by the ammonium molybdate spectrophotometric method. The results are as shown in Figure 6 the figure. From Figure 6 it can be seen that the adsorption rate of Sample 1 in Example 1 of this application is affected to a certain extent. Sample 1 basically reached the adsorption equilibrium at 30 minutes of adsorption but still could reduce the phosphorus concentration from 2 mg / L to below 0.1 mg / L, indicating that it is not greatly affected by high-concentration coexisting ions and has strong selectivity for phosphate.

[0052] Prepare a series of potassium dihydrogen phosphate solutions with phosphorus concentrations ranging from 5 to 50 mg / L. According to the dosage ratio of 1 g adsorbent per 1 L potassium dihydrogen phosphate solution, sample one in Example 1 and sample two in Comparative Example 1 were respectively added to the potassium dihydrogen phosphate solutions and adsorbed for 24 h at a temperature of 25 °C and a rotation speed of 180 rpm. Use a disposable syringe to take the supernatant, filter it through a 0.45 μm aqueous filter membrane, and determine the equilibrium phosphorus concentration by the ammonium molybdate spectrophotometric method. Draw an isothermal adsorption equation fitting curve graph based on the results, and the results are as Figure 7 shown. According to the fitting results of the Langmuir model, the adsorption capacity of sample one is 14.3 mg / g, and the adsorption capacity of sample two is 6.0 mg / g, indicating that after amine modification, the adsorption capacity has been significantly improved, reaching more than twice that of the unmodified material.

[0053] The substance leaching conditions of sample one in Example 1, sample two in Comparative Example 1, and sample three in Comparative Example 2 after shaking in the potassium dihydrogen phosphate solution for 24 h are as Figure 8 shown. From Figure 8 it can be seen that the organic matter leaching concentration and iron ion leaching concentration of sample one in Example 1 of the present invention are the lowest, and are far lower than the pollutant discharge standards of urban sewage treatment plants, indicating that its secondary pollution risk is small, it has environmental friendliness, and can be applied in practice.

[0054] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A preparation method of amine-modified magnetite for phosphorus removal from wastewater, characterized in that, It includes the following steps: S1. Dissolve iron acetylacetonate and long-chain organic amine in absolute ethanol to obtain a dark red clear solution; subject 1-octadecene to a constant temperature water bath for later use; S2. Under stirring, slowly drop the dark red clear solution into the 1-octadecene and continue the constant temperature water bath to obtain a mixed solution; S3. Transfer the mixed solution into a reaction kettle and obtain a black mixture after high-temperature reaction in an inert atmosphere; S4. Subject the black mixture to magnetic separation, washing, and freeze-drying in sequence to obtain amine-modified iron oxide.

2. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S1, the long-chain organic amine includes at least one of octadecylamine, N-methyloctadecylamine, and N,N-dimethyloctadecylamine.

3. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S1, the molar ratio of iron acetylacetonate to long-chain organic amine is 1:0.5 - 3.

4. The preparation method of amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S2, the volume ratio of 1-octadecene to the dark red clear solution is 1:0.1 - 0.

4.

5. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S2, the temperature of the constant temperature water bath is 75 - 100 °C, and the time is 1 - 2 h; the rate of slow dropping is 1 - 5 mL / min.

6. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S3, the temperature of the high-temperature reaction is 160 - 220 °C, and the time is 5 - 24 h.

7. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S3, the inert atmosphere is at least one of nitrogen and argon.

8. The preparation method of the amine-modified magnetite for phosphorus removal from wastewater according to claim 1, characterized in that, In step S3, the washing is to wash successively with an organic detergent and deionized water multiple times respectively; the detergent includes absolute ethanol and hexane; the time of freeze-drying is 6 - 24 h.

9. An amine-modified iron oxide for phosphorus removal from wastewater prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the amine-modified iron oxide for phosphorus removal from wastewater according to claim 9 in deep adsorption and phosphorus removal in sewage.

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