Preparation method of strong magnetic iron-based flocculant and efficient phosphorus removal application thereof

Abstract

The application relates to the technical field of water treatment materials, in particular to a preparation method of a strong magnetic iron-based flocculant and efficient phosphorus removal application of the strong magnetic iron-based flocculant. The preparation method of the strong magnetic iron-based flocculant comprises the following steps: iron salt solution is added into oxalic acid solution and stirred until yellow precipitate appears, then the mixture is placed, and the oxalic acid ferrous precursor is obtained through filtration, washing and drying in sequence; the oxalic acid ferrous precursor is subjected to plasma treatment to obtain the strong magnetic iron-based flocculant. The application provides an environment-friendly, low-temperature and high-efficiency synthesized iron-based flocculant, which is suitable for efficient removal of phosphorus in sewage and eutrophic water bodies, and solves the problems of large pollution and low phosphorus removal efficiency in traditional processes.

Description

Technical Field

[0001] This invention relates to the field of water treatment materials technology, and in particular to a method for preparing a strongly magnetic iron-based flocculant and its efficient phosphorus removal application. Background Technology

[0002] Eutrophication of water bodies has become a global environmental problem, with phosphorus, as a key limiting nutrient, mainly originating from domestic sewage, agricultural runoff, and industrial wastewater. Although traditional phosphorus removal technologies such as chemical precipitation (using aluminum and calcium salts), biological methods, and adsorption are widely used, they generally have significant drawbacks: aluminum salt flocculants can easily lead to residual aluminum ions causing neurotoxicity risks, and sludge disposal is difficult; calcium salt phosphorus removal is limited by high pH requirements and pipe scaling problems; while biological methods have lower operating costs, they suffer from bottlenecks such as weak resistance to shock loads and a sharp drop in efficiency at low temperatures. Iron-based flocculants (such as ferric chloride and ferrous sulfate) are gradually becoming the mainstream choice due to the environmental friendliness, low cost, and high phosphorus removal efficiency of iron (through the formation of FePO4 precipitate and complexation adsorption). However, existing iron-based flocculants still face three major technical challenges: First, traditional synthesis processes rely on strong acid media (such as concentrated hydrochloric acid activation) or high-temperature reactions (>100℃), leading to high energy consumption, equipment corrosion, and the generation of toxic byproducts (such as chlorinated hydrocarbons), violating the principles of green chemistry. Second, conventional iron salts are easily hydrolyzed over a wide pH range (especially under alkaline conditions) to form colloidal Fe(OH)3, resulting in the loss of effective components and a reduction in phosphorus adsorption capacity; moreover, the flocculation effect deteriorates significantly at low temperatures. Third, organic additives (such as polyacrylamide) introduced to improve stability may cause secondary pollution and increase the COD load of water bodies. In recent years, green synthesis pathways have become an important direction for the research and development of iron-based flocculants. Therefore, developing an iron-based flocculant that can be synthesized efficiently under mild conditions, without toxic additives, and with wide pH adaptability has become an urgent need to overcome the bottleneck in phosphorus pollution control. Summary of the Invention

[0003] The purpose of this invention is to provide a strongly magnetic iron-based flocculant based on a green synthesis process and its application, thereby addressing the problems existing in the prior art. The strongly magnetic iron-based flocculant prepared by this invention can be used as a flocculant to generate insoluble iron phosphate precipitate through a chemical precipitation-adsorption synergistic mechanism, thus achieving efficient removal of phosphorus from eutrophic water bodies.

[0004] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a strongly magnetic iron-based flocculant, comprising the following steps: The iron salt solution was added to the oxalic acid solution and stirred until a yellow precipitate appeared. After standing, the solution was filtered, washed, and dried to obtain the ferrous oxalate precursor. The ferrous oxalate precursor was subjected to plasma treatment to obtain the strongly magnetic iron-based flocculant.

[0005] The second technical solution of the present invention is a strongly magnetic iron-based flocculant prepared according to the above preparation method.

[0006] The third technical solution of this invention is the application of the above-mentioned strong magnetic iron-based flocculant in the treatment of phosphorus-containing wastewater.

[0007] The fourth technical solution of the present invention is a method for treating phosphorus-containing wastewater, which involves adding the above-mentioned strongly magnetic iron-based flocculant to the phosphorus-containing wastewater for flocculation, thereby removing phosphorus from the wastewater.

[0008] This invention provides an environmentally friendly, low-temperature, and highly efficient iron-based flocculant suitable for the efficient removal of phosphorus from wastewater and eutrophic water bodies, solving the problems of high pollution and low phosphorus removal efficiency in traditional processes.

[0009] The present invention discloses the following technical effects: (1) The strong magnetic iron-based flocculant prepared by the present invention can be used as a flocculant to achieve efficient, rapid and stable capture of phosphate, and is suitable for effective removal of phosphorus in complex water bodies.

[0010] (2) The strong magnetic iron-based flocculant of the present invention achieves efficient phosphorus removal through a triple synergistic effect due to its unique surface chemical properties. It has high adsorption performance and pH stability for phosphorus in water, and has good application prospects in the treatment of eutrophic wastewater. Furthermore, the preparation conditions of the strong magnetic iron-based flocculant of the present invention are mild, the process is simple, the operation is quick, and it is environmentally friendly.

[0011] (3) The main raw material for preparing the strong magnetic iron-based flocculant of the present invention is oxalic acid (ethanedioic acid). As a widely available and biodegradable natural organic acid, it has a high cost-performance ratio and practicality, and shows the unique advantage of being used as an environmentally friendly raw material for the synthesis of iron-based flocculants.

[0012] (4) The strong magnetic iron-based flocculant of the present invention has the characteristics of being inexpensive, efficient, non-toxic, environmentally friendly and easy to mass-produce. It can quickly remove phosphorus species that are difficult to remove from water, thereby achieving the effect of protecting and purifying the environment.

[0013] (5) The strong magnetic iron-based flocculant of the present invention is activated by argon plasma. The ferrous oxalate precursor is placed in an argon plasma tube furnace, and the solid-phase transformation of the flocculant is achieved by non-equilibrium high-energy electron bombardment, thereby increasing the surface active sites of the flocculant. It also achieves zero solvent / zero additives and ultra-low energy consumption, saving 80% more energy than traditional calcination. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a SEM image of the strongly magnetic iron-based flocculant prepared in Example 1 of the present invention; Figure 2 XRD patterns of the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 and the flocculant (MF) prepared in Example 2 of this invention; Figure 3 This is a graph showing the efficiency of the strongly magnetic iron-based flocculant prepared in Example 1 of the present invention in adsorbing phosphorus in water. Figure 4 The X-ray photoelectron spectroscopy (XPS) test results are for the strongly magnetic iron-based flocculant prepared in Example 1 of this invention. Figure 5 The graph shows the efficiency of the strongly magnetic iron-based flocculant prepared in Example 1 of this invention in adsorbing phosphorus in water under different pH conditions. Detailed Implementation

[0016] 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.

[0017] 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. Any stated value or intermediate value within a stated range, as well as each smaller range between 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.

[0018] 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.

[0019] 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 apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0020] 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.

[0021] The first aspect of this invention provides a method for preparing a strongly magnetic iron-based flocculant, comprising the following steps: Add the iron salt solution to the oxalic acid solution and stir until a yellow precipitate appears (Fe during the reaction). 2+ The ions undergo a metathesis reaction with C2H2O4, through the exchange of ions, Fe... 2+ With H + Exchange ligand SO4 2- With C2O4 2- (A yellow FeC2O4 precipitate was formed), and after standing, the mixture was filtered, washed, and dried sequentially to obtain the ferrous oxalate precursor. The ferrous oxalate precursor was subjected to plasma treatment to obtain the strongly magnetic iron-based flocculant.

[0022] In a preferred embodiment of the present invention, the iron salt solution is a 0.1M ferrous sulfate solution.

[0023] In a preferred embodiment of the present invention, the concentration of the oxalic acid solution is 0.1M and the pH is 3-3.5.

[0024] In this invention, the pH of the oxalic acid solution affects the crystallinity of the synthesized ferrous oxalate, which in turn affects the phosphorus removal effect of the final prepared strong magnetic iron-based flocculant. Therefore, this invention preferably limits the pH of the oxalic acid solution to 3-3.5.

[0025] If the concentration of iron salt solution and oxalic acid solution is too high, they will form a saturated solution, which will not be able to dissolve the oxalic acid and iron salt.

[0026] In a preferred embodiment of the present invention, the volume ratio of the iron salt solution to the oxalic acid solution is 1:1.

[0027] In a preferred embodiment of the present invention, the settling time is 7 to 12 hours.

[0028] In this invention, the purpose of allowing the mixture to stand is that since the reaction is a metathesis precipitation reaction, a short time is not conducive to the formation of a precipitate. Under low temperature conditions, the time can be appropriately extended so that the reaction can proceed completely.

[0029] In a preferred embodiment of the present invention, the drying process specifically involves vacuum drying at 60-70°C for 12-24 hours.

[0030] In a preferred embodiment of the present invention, the plasma treatment conditions are set as follows: the treatment atmosphere is high-purity Ar, the radio frequency power is 100-500W (preferably 300W), the gas flow rate is 10-20mL / s (preferably 20mL / s), and the treatment time is 10min.

[0031] In this invention, if the radio frequency power of the plasma treatment exceeds 500W, the material may be carbonized at high temperatures due to the increased power generated by the high-energy active atmosphere; radio frequency power below 100W cannot sufficiently activate the surface of ferrous oxalate in its active atmosphere. Therefore, this invention preferably limits the radio frequency power of the plasma treatment to the above-mentioned parameter range.

[0032] A second aspect of the present invention provides a strongly magnetic iron-based flocculant prepared according to the above-described preparation method.

[0033] The third aspect of this invention provides the application of the above-mentioned strongly magnetic iron-based flocculant in the treatment of phosphorus-containing wastewater.

[0034] The fourth aspect of this invention provides a method for treating phosphorus-containing wastewater, wherein the above-mentioned strongly magnetic iron-based flocculant is added to the phosphorus-containing wastewater for flocculation, thereby removing phosphorus from the wastewater.

[0035] The strong magnetic iron-based flocculant of the present invention can achieve efficient removal of phosphorus from water, with a phosphorus removal rate of >95% (initial phosphorus concentration 10 mg / L, dosage 200 mg / L).

[0036] This invention uses ferrous sulfate (FeSO4) as the iron source, reacting it with oxalic acid (C2H2O4) at room temperature and pressure to generate ferrous oxalate precipitate. The process conditions are mild, requiring no strong acid / high temperature, with low energy consumption and no harmful byproducts. Furthermore, the ferrous oxalate precursor is activated in the solid phase through argon plasma treatment. This allows for precise control of the flocculant structure and activity under solvent-free and chemical additive-free conditions, completely avoiding the energy consumption and waste gas emissions of traditional high-temperature calcination, achieving a fully green synthesis process. The resulting flocculant possesses a high specific surface area and abundant active sites, achieving efficient phosphorus removal from water bodies and showing promising application prospects in the treatment of eutrophic water bodies.

[0037] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0038] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0039] Example 1 A method for preparing a strongly magnetic iron-based flocculant: (1) Dissolve ferrous sulfate heptahydrate (FeSO4·7H2O) and oxalic acid (C2H2O4·2H2O) in 100mL of deionized water to obtain a 0.1M ferrous sulfate solution and a 0.1M oxalic acid solution (adjust the pH of the oxalic acid solution to 3~3.5 with ammonia). Add the prepared ferrous sulfate solution dropwise to the oxalic acid solution at a rate of 3ml / s while stirring until a yellow precipitate appears. Let it stand for 7h.

[0040] (2) The yellow precipitate prepared in (1) was filtered, washed and dried under vacuum at 60°C for 12 h to obtain ferrous oxalate (β-FeC2O4) precursor.

[0041] (3) Take out the ferrous oxalate precursor prepared in step (2) and place it in a plasma tube furnace. Under the atmosphere of argon, at a gas flow rate of 20 mL / s and a plasma power of 300 W for 10 min, a strong magnetic iron-based flocculant (PL300W) is obtained.

[0042] Example 1 The SEM image of the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 of this invention is shown below. Figure 1 .

[0043] from Figure 1 As can be seen, the material surface possesses a highly developed multi-level micro / nano structure. This non-smooth morphology with a high specific surface area greatly increases the number of lattice defect sites, is rich in unsaturated bonds, surface hydroxyl groups, or specific functional groups, constituting a large number of potential chemisorption active sites, providing ample space for phosphate anchoring. The microporous and mesoporous structures can effectively retain phosphate ions, while the hierarchical channels promote rapid diffusion and mass transfer of the solution within the material, ensuring efficient utilization of adsorption sites. This reduces ion diffusion resistance while achieving rapid adsorption kinetics.

[0044] Example 2 The phosphorus removal performance of the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 of this invention was determined.

[0045] (1) Dissolve 0.1 g of potassium dihydrogen phosphate (KH2PO4) in 100 mL of deionized water and stir ultrasonically until dissolved. Then transfer it to a volumetric flask with a volume of 1 L, make up to volume and sonicate until homogeneous to obtain a target pollutant mother liquor with a concentration of 100 mg / L of potassium dihydrogen phosphate.

[0046] (2) Preparation of colorimetric reagent: Add 0.35g of potassium antimony tartrate (C8H4K2O) 12Sb·1 / 2H2O) and 13g of ammonium molybdate ((NH4)2MoO4·4H2O) were dissolved in 100mL of deionized water and ultrasonically stirred until dissolved. 150mL of concentrated sulfuric acid was added to 150mL of deionized water and cooled to room temperature. The ammonium molybdate solution was then added to the H2SO4 solution and stirred until homogeneous. Potassium antimony tartrate solution was then added and stirred until homogeneous. The solution was then transferred to a 500mL volumetric flask, diluted to volume, and ultrasonically homogenized to obtain the molybdate colorimetric reagent.

[0047] Dissolve 10g of ascorbic acid (C6H8O6) in 100mL of deionized water and sonicate until dissolved.

[0048] A 50 mL solution of 10 mg / L potassium dihydrogen phosphate was prepared as the target pollutant. The flocculant PL300W prepared in Example 1 of this invention was used as the phosphorus removal flocculant. The flocculant dosage was 200 mg / L. The flocculation process was carried out by stirring at a stirring rate of 250 rpm. The test conditions were: pH 6.86 and room temperature (25°C). The phosphorus content was detected at 2 min, 5 min, 10 min and 20 min of flocculation.

[0049] Detection: The solution was drawn into a 2.5ml syringe and filtered through a 0.25μL nylon filter. Ascorbic acid and molybdate solutions were then added for color development. After adding 5% ascorbic acid solution and 5% molybdate solution respectively, the mixture was sonicated for 15 min. The phosphorus content was then detected using a UV-Vis spectrophotometer at a wavelength of 700nm. The test results are as follows: Figure 3 .

[0050] Figure 3 The Y-axis corresponds to the residual percentage content of the phosphate solution at adsorption reaction time t (X-axis). From... Figure 3 As can be seen, when the flocculant (PL300W) prepared in Example 1 of this invention is used as the phosphorus removal flocculant, the phosphate is basically completely removed after the adsorption reaction has proceeded for 20 minutes, with a removal rate of up to 100%. This is because the huge specific surface area and abundant active sites of this invention directly increase the upper limit of phosphate loading per unit mass of material. Through coordination exchange and the formation of inner layer complexes, it specifically and strongly binds to phosphate, ensuring the strong adsorption, and is suitable for the remediation of phosphorus pollution in water bodies.

[0051] Based on the phosphorus removal experiment in Example 2, this invention also tested the phosphorus removal effect of PL300W under pH conditions of 3, 4, 5, 6, 7, 8, 9, and 10 (i.e., the only difference from the phosphorus removal experiment test conditions above was adjusting the pH to 3, 4, 5, 6, 7, 8, 9, or 10). The results are as follows: Figure 5 As shown, by Figure 5It can be seen that the flocculant prepared in Example 1 of the present invention can achieve a removal rate of more than 85% under a wide pH range.

[0052] Based on the phosphorus removal experiment in Example 2, this invention also tested the phosphorus removal effect when other pollutants were present in the water. The results showed that in the presence of multiple other anions, such as SO42-, the phosphorus removal effect was significantly improved. 2- When anions are present, the flocculant can remove more than 85% of phosphorus from water.

[0053] X-ray photoelectron spectroscopy (XPS) was performed on the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 of this invention. The results are shown in [Figure 1]. Figure 4 .

[0054] Depend on Figure 4 As can be seen from the data, the strongly magnetic iron-based flocculant (PL300W) prepared in this invention exhibits a significant P2p characteristic peak after adsorption, proving that phosphorus elements were successfully captured on the material surface.

[0055] Example 2 The only difference from Example 1 is that in step (3), the ferrous oxalate (FeC2O4) precursor is placed in a muffle furnace and heated to 250°C at a heating rate of 2°C / s, and held for 2 hours to obtain flocculant MF.

[0056] The XRD patterns of the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 and the flocculant (MF) prepared in Example 2 of this invention were determined, and the results are as follows: Figure 2 As shown.

[0057] Depend on Figure 2 It can be seen that the strongly magnetic iron-based flocculant (PL300W) prepared in Example 1 corresponds to the JCPDS standard card information of γ-Fe2O3, indicating that the present invention has successfully prepared a green-synthesized magnetic iron-based flocculant. The flocculant MF prepared in Example 2 corresponds to the JCPDS standard card information of α-Fe2O3. Moreover, the strongly magnetic iron-based flocculant (PL300W) prepared in the present invention has low crystallinity, which may expose more surface defects and dangling bonds, significantly increasing the density of active sites. At the same time, the low crystallinity material has a high density of hydroxyl (-OH) on the surface, and the coordination unsaturation of iron metal sites is stronger. It can form a stable Fe-OP inner-layer complex with phosphate through ligand exchange, thereby significantly enhancing the chemical adsorption affinity.

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. The application of a strongly magnetic iron-based flocculant in the treatment of phosphorus-containing wastewater, characterized in that, The preparation method of the strongly magnetic iron-based flocculant includes the following steps: The iron salt solution was added to the oxalic acid solution and stirred until a yellow precipitate appeared. After standing, the solution was filtered, washed, and dried to obtain the ferrous oxalate precursor. The ferrous oxalate precursor was subjected to plasma treatment to obtain the strongly magnetic iron-based flocculant. The plasma treatment conditions are set as follows: the treatment atmosphere is high-purity Ar, the radio frequency power is 100-500W, the gas flow rate is 10-20mL / s, and the treatment time is 10min.

2. The application according to claim 1, characterized in that, The iron salt solution is a 0.1M ferrous sulfate solution.

3. The application according to claim 1, characterized in that, The concentration of the oxalic acid solution is 0.1M.

4. The application according to claim 1, characterized in that, The volume ratio of the iron salt solution to the oxalic acid solution is 1:

1.

5. The application according to claim 1, characterized in that, The settling time is 7-12 hours.

6. The application according to claim 1, characterized in that, The drying process specifically involves vacuum drying at 60-70℃ for 12-24 hours.

7. The application according to claim 1, characterized in that, Adding a strong magnetic iron-based flocculant to phosphorus-containing wastewater can achieve flocculation and thus remove phosphorus from the wastewater.

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