FePO4 composite nano-material for removing ammonia nitrogen in sewage and preparation method of FePO4 composite nano-material
By preparing FePO4 composite nanomaterials, the electrostatic effects of sulfonic acid-modified polystyrene microspheres and FePO4 nanoparticles were solved, and the problems of poor selectivity for ammonia nitrogen removal and limited adsorption capacity in the prior art were achieved, and efficient and stable deep purification effect of ammonia nitrogen was achieved.
Patent Information
- Application Number
- CN202510686934.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-27
- Publication Date
- 2025-07-11
AI Technical Summary
The existing wastewater treatment technology is difficult to remove ammonia nitrogen efficiently and economically. Commonly used materials have poor selectivity for ammonia nitrogen, limited adsorption capacity, and complex and poor stability in the preparation process, which cannot meet the needs of deep purification.
Using sulfonic acid-modified polystyrene microspheres as support, FePO4 composite nanomaterials were prepared through ion exchange and electrostatic action of FePO4 nanoparticles, achieving high selective adsorption of ammonia nitrogen, and combining hydrogen bonds and chemical precipitation to form Fe-NH4-PO4 complexes.
It has achieved efficient deep purification of ammonia nitrogen in wastewater, strong adsorption selectivity, good stability, renewable and recyclable materials, and meet relevant emission standards.
Smart Images
Figure CN120285961A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a FePO4 composite nanomaterial for removing ammonia nitrogen from sewage, and also relates to a preparation method of the above composite nanomaterial. Background Art
[0002] Excessive ammonia nitrogen in water can lead to eutrophication of water bodies, cause a large number of algae to multiply, and damage the ecological balance of water bodies; at the same time, it can inhibit the metabolic functions of aquatic organisms, cause acute poisoning and chronic tissue damage to fish; it can also generate nitrites and nitrates through nitrification, threatening the safety of drinking water. For human health, ammonia nitrogen can accumulate through the food chain, leading to damage to organs such as the human liver and kidneys. Long-term intake of drinking water with excessive nitrate content can induce methemoglobinemia. Therefore, effectively removing ammonia nitrogen from sewage is of great significance for protecting the water environment and human health.
[0003] Currently, the commonly used ammonia nitrogen wastewater treatment technologies mainly include: biological methods (such as A / O process, biofilm reactor, etc.) and physical and chemical methods (such as stripping method, chemical oxidation, chemical precipitation and adsorption method, etc.). Biological nitrogen removal realizes the conversion and removal of ammonia nitrogen through two stages of nitrification and denitrification. Although it has good economy, it is easily restricted by factors such as dissolved oxygen, water temperature, and sludge age, with a long treatment cycle and poor adaptability to high-concentration ammonia nitrogen wastewater. The stripping method has high energy consumption and a risk of ammonia gas escape. The chemical oxidation method directly oxidizes ammonia nitrogen into nitrogen gas or harmless substances through strong oxidants, which is suitable for emergency treatment or scenarios where the ammonia nitrogen concentration in the effluent fluctuates greatly. However, especially because it requires the addition of chemical agents, the operating cost is relatively high. The chemical precipitation method generates magnesium ammonium phosphate precipitate by adding magnesium salts and phosphates and reacting with ammonia nitrogen, which has a significant effect on high-concentration ammonia nitrogen wastewater, but the reagent cost is relatively high, and the precipitation by-products need to be treated. In contrast, the adsorption method has attracted much attention due to its simple operation, stable operation, and suitability for advanced denitrification. This technology directly captures ammonia nitrogen molecules through physical adsorption or ion exchange, and is especially suitable for the upgrading of low-concentration tail water, becoming a key supplementary means for advanced sewage treatment.
[0004] Currently, the commonly used adsorption materials mainly include: activated carbon, zeolite, nanomaterials, etc. Activated carbon has a developed microporous structure and a relatively high specific surface area, but has poor selectivity for ammonia nitrogen and limited adsorption capacity; zeolite has good ion exchange performance, but coexisting cations (such as calcium, magnesium, etc.) will significantly reduce the treatment efficiency. Emerging nanomaterials, such as carbon nanotubes and graphene, although having relatively high adsorption potential, have weak chemical binding force to ammonia nitrogen due to the lack of surface functional groups. Metal-organic framework (MOFs) materials have a tunable pore structure, but the complex preparation process and poor stability restrict their practical applications. Summary of the Invention
[0005] Object of the Invention: The object of the present invention is to provide an FePO4 composite nanomaterial with a fast adsorption rate, high adsorption capacity, and strong selectivity, which can achieve efficient and deep purification of ammonia nitrogen in sewage; another object of the present invention is to provide a preparation method of the above FePO4 composite nanomaterial.
[0006] Technical Solution: The FePO4 composite nanomaterial for removing ammonia nitrogen in sewage according to the present invention has a sulfonic acid group-modified polystyrene microsphere as a carrier, and FePO4 nanoparticles are immobilized in the pores of the polystyrene microsphere.
[0007] Among them, the particle size of the FePO4 nanoparticles immobilized in the pores of the polystyrene microsphere is 10 - 40 nm; in the composite nanomaterial, the content of FePO4 is 4 - 10% (calculated by the mass percentage of Fe in the composite nanomaterial); the particle size of the composite nanomaterial is 0.5 - 1.2 mm, and the average pore diameter is about 5 - 20 nm.
[0008] Among them, the sulfonic acid group-modified polystyrene microsphere has a styrene-divinylbenzene copolymer as the basic skeleton, and sulfonic acid groups (-SO3H) are bonded to the skeleton, and the content of the sulfonic acid groups ≥ 4 mmol / g (compared with the polystyrene microsphere); the particle size of the polystyrene microsphere is 0.5 - 1.2 mm, and the average pore diameter is 20 - 40 nm, and its chemical structural formula is:
[0009]
[0010] In the structure, the strongly negatively charged sulfonic acid groups can achieve the adsorption of ammonia nitrogen through ion exchange and electrostatic interaction.
[0011] The preparation method of the above FePO4 composite nanomaterial includes the following steps:
[0012] (1) Dissolve analytical pure Fe(NO3)3·9H2O in an aqueous solution of ethanol to obtain a mixed solution, and adjust the pH of the solution to ≤ 1.0 with HNO3 to prevent the hydrolysis of Fe(NO3)3 in the solution and affect the pre-loading amount of the Fe(III) precursor in the carrier;
[0013] (2) Add the sulfonic acid group-modified polystyrene microspheres to the mixed solution in step (1), control the dosage of the polystyrene microspheres to be 100 - 200 g / L, and stir and react at 15 - 25 °C for 12 h; during this process, Fe(III) is pre-loaded in the pores of the sulfonic acid group-modified polystyrene microspheres in the form of a precursor through ion exchange; during this process, the reaction temperature should not be too high to prevent the hydrolysis of Fe(NO3)3 due to the accelerated volatilization of HNO3; at the same time, the reaction temperature should not be too low to avoid too low reaction rate affecting the loading amount of the Fe(III) precursor;
[0014] (3) Dilute phosphoric acid (analytical pure) with a concentration of 85 wt% with ultrapure water (resistivity ≥ 18.2 MΩ·cm) to a phosphoric acid solution with a concentration of 0.2 - 0.5 mol / L; the concentration of the phosphoric acid solution should not be too high or too low to avoid overly violent subsequent reactions or insufficient reaction rates.
[0015] (4) Filter out the polystyrene microspheres pre-loaded with Fe(III) in step (2), slowly add them to the phosphoric acid solution in step (3), and stir and react at 60 - 70 °C for 3 - 6 h. The dosage of the polystyrene microspheres pre-loaded with Fe(III) is 100 - 200 g / L; use 1 mol / L NaOH and 1 mol / L HNO3 solutions to control the pH of the reaction system to be within the range of 2 ± 0.2, so that FePO4 nanoparticles are deposited in the pores of the polystyrene microspheres; controlling the pH within the range of 2 ± 0.2 can inhibit the hydrolysis of Fe(III) ions to form Fe(OH)3 and avoid the formation of Fe2(HPO4)3 at the same time, ensuring the preferential precipitation of FePO4.
[0016] (5) Filter out the polystyrene microspheres after the reaction in step (4), first rinse them thoroughly with 1 mol / L KCl solution, then wash them with deionized water until the conductivity of the effluent is < 50 μS / cm (to remove all residual ions after the reaction and rinsing with KCl solution to ensure the purity of the finally prepared material), and finally soak them with absolute ethanol and place them in a vacuum drying oven, and vacuum dry at 80 °C for 12 h to obtain the FePO4 composite nanomaterial. The purpose of washing with KCl solution is to remove the unreacted reagents in the pores of the material, and soaking with absolute ethanol is to displace the residual water in the pores of the polystyrene to facilitate subsequent drying; among them, the drying temperature is 80 °C. If the drying temperature is too high, it will cause partial shedding of sulfonic acid groups and affect the adsorption performance of the material.
[0017] Among them, in step (1), the ethanol aqueous solution is obtained by adding ultrapure water (resistivity ≥ 18.2 MΩ·cm) to absolute ethanol; in the ethanol aqueous solution, the volume of ethanol accounts for 5 - 10% of the total volume of the solution; in the mixed solution, the concentration of Fe(NO3)3·9H2O is 0.2 - 0.5 mol / L.
[0018] In step (4), during the reaction process, the reaction system is mechanically stirred with a polytetrafluoroethylene stirring paddle, and the stirring speed is controlled to be ≥ 600 rpm to ensure that the entire reaction system is in a homogeneous state.
[0019] The FePO4 composite nanomaterial of the present invention uses sulfonic acid group-modified polystyrene microspheres as the carrier and Fe(NO3)3 as the precursor, and through the "Fe(III) ion pre-loading - in-situ deposition of phosphoric acid" process, FePO4 is deposited in the pores of the polystyrene microspheres in the form of nanoparticles.
[0020] The application of the above FePO4 composite nanomaterial as an adsorbent in sewage denitrification. The specific application process is as follows: The sewage with excessive ammonia nitrogen is introduced into a precision filter, and the obtained filtrate passes through an adsorption tower filled with the FePO4 composite nanomaterial, so that the ammonia nitrogen in the sewage is selectively adsorbed and removed by the composite nanomaterial; when the ammonia nitrogen concentration in the effluent after the treatment of the adsorption tower reaches the adsorption end point, the water inlet of the adsorption tower is stopped, and the FePO4 composite nanomaterial is desorbed and regenerated with a KCl solution. After regeneration, the composite nanomaterial can be reused; the obtained desorption liquid can realize ammonia nitrogen recovery through magnesium ammonium phosphate precipitation.
[0021] In the sewage with excessive ammonia nitrogen, the ammonia nitrogen concentration is 5.0 - 20.0 mg / L, and the pH is 6 - 8. At this time, the ammonia nitrogen in the sewage mainly exists in the form of ammonium ions (NH4 + ).
[0022] During the adsorption process, the polystyrene microsphere carrier realizes the rapid enrichment of ammonia nitrogen in the sewage from the main solution to the surface of the composite nanomaterial liquid film through the Donnan membrane pre - enrichment effect of the strongly negatively charged sulfonic acid groups on the surface, greatly increasing the ammonia nitrogen concentration on the liquid film surface and improving the mass transfer rate; the FePO4 nanoparticles loaded in the composite nanomaterial realize the selective adsorption of ammonia nitrogen in the sewage through the comprehensive action of hydrogen bonding, electrostatic attraction and chemical precipitation.
[0023] After the sewage removes suspended solid particles through the precision filter, the filtrate is passed through the adsorption tower filled with the FePO4 composite nanomaterial from top to bottom, and the hydraulic retention time is controlled to be 6 - 12 min. The ammonia nitrogen in the sewage is selectively adsorbed on the composite nanomaterial, and the ammonia nitrogen concentration in the adsorption effluent < 1.0 mg / L, meeting the requirements of relevant regional sewage discharge standards such as "Discharge Standards for Pollutants from Municipal Wastewater Treatment Plants (DB32 / 4440 - 2022)" and "Discharge Standards for Water Pollutants from Municipal Wastewater Treatment Plants (DB11 / 890 - 2012)".
[0024] When the ammonia nitrogen in the effluent of the adsorption tower ≥ 1.0 mg / L, the water inlet of the adsorption tower is stopped. At this time, the adsorption bed layer reaches the breakthrough point and needs to be regenerated to restore its adsorption capacity for recycling. A KCl solution with a concentration of 1 - 2 mol / L is passed through the adsorption tower from top to bottom to in - situ desorb and regenerate the FePO4 composite nanomaterial saturated with adsorption, and the hydraulic retention time is controlled to be 60 - 120 min.
[0025] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) In the FePO4 composite nanomaterial of the present invention, the sulfonic acid group-modified polystyrene microspheres can achieve the adsorption of ammonia nitrogen through ion exchange and electrostatic interaction; the loaded FePO4 nanoparticles can achieve the highly selective adsorption of ammonia nitrogen in sewage through the combined action of hydrogen bonding, electrostatic attraction, and chemical precipitation (forming iron ammonium phosphate complex with ammonia nitrogen); its adsorption selectivity mainly stems from the fact that FePO4 can react with ammonia nitrogen to form Fe-NH4-PO4 complex, and the coexisting cations such as Na + 、K + 、Ca 2+ 、Mg 2+ in the solution have little inhibitory effect on this adsorption mechanism, thus achieving highly selective adsorption. (2) The negatively charged sulfonic acid groups modified on the surface of the carrier polystyrene microspheres can achieve the rapid capture of low-concentration ammonia nitrogen in sewage through their unique Donnan membrane pre-concentration effect, so that the composite material exhibits excellent ammonia nitrogen deep purification performance. (3) The FePO4 composite nanomaterial of the present invention has strong stability and can be used stably for a long time under the condition of pH 3-10, and the loaded FePO4 nanoparticles do not dissolve out; and the material has good regeneration performance and can be recycled for a long time. Description of the Drawings
[0026] Figure 1 are photos of the sulfonic acid group-modified polystyrene microspheres used in Example 2 and the FePO4 composite nanomaterial prepared in Example 2; among them, a is the sulfonic acid group-modified polystyrene microspheres, and b is the FePO4 composite nanomaterial;
[0027] Figure 2 is the cross-sectional SEM-EDS diagram of the FePO4 composite nanomaterial prepared in Example 2;
[0028] Figure 3 is the TEM diagram of the FePO4 composite nanomaterial prepared in Example 2;
[0029] Figure 4 is the stability of the FePO4 composite nanomaterial prepared in Example 2 under different pH conditions;
[0030] Figure 5 is the process flow diagram of applying the FePO4 composite nanomaterial of the present invention to the deep removal of ammonia nitrogen from sewage. Detailed Embodiments
[0031] Example 1
[0032] The preparation method of the FePO4 composite nanomaterial of the present invention includes the following steps:
[0033] (1) Fe(NO3)3·9H2O was fully dissolved in an aqueous solution containing 5% (V / V) ethanol, the concentration of Fe(NO3)3·9H2O was controlled to be 0.2 mol / L, and the pH of the solution was adjusted to ≤1.0 with HNO3; sulfonic acid group-modified polystyrene microspheres were added to the mixed solution, the dosage of polystyrene microspheres was 100 g / L, and the reaction was stirred at 15°C for 12 h to obtain polystyrene microspheres preloaded with Fe(III);
[0034] (2) The polystyrene microspheres preloaded with Fe(III) were filtered out and slowly added into a 0.2 mol / L phosphoric acid solution, and stirred at 70°C for 3 h. The amount of the polystyrene microspheres preloaded with Fe(III) was 100 g / L. The pH of the reaction system was controlled to be within the range of 2±0.2 using 1 mol / L NaOH and 1 mol / L HNO3 solutions.
[0035] (3) The polystyrene microspheres after the reaction were filtered out, first rinsed thoroughly with 1 mol / L KCl solution, then washed with deionized water until the outlet water conductivity was <50 μS / cm, and finally soaked with anhydrous ethanol and placed in a vacuum drying oven, and vacuum dried at 80°C for 12 h to obtain FePO4 composite nanomaterials.
[0036] The composite nanomaterial prepared in Example 1 has a particle size of 0.5-1.2 mm, a pore size distribution of 5-20 nm, and a particle size of the FePO4 nanoparticles loaded in the pores of 10-40 nm; in the composite nanomaterial, the content of FePO4 is 4 wt.% (in terms of mass percentage of Fe).
[0037] The wastewater with excessive ammonia nitrogen (ammonia nitrogen concentration of 7.8 mg / L, pH of 7.5) was introduced into a precision filter. The filter used a polypropylene hot-sprayed fiber membrane filter element with a filtration accuracy of 1 μm, a filtration pressure of 0.4 MPa, an outlet turbidity of ≤0.1 NTU, and a sludge density index SDI ≤5.
[0038] 5mL of FePO4 composite nanomaterial prepared in Example 1 was loaded into an adsorption column (16×160mm), and the filtrate was passed from top to bottom through the composite nanomaterial adsorption bed at a flow rate of 50mL / h (hydraulic retention time of 6min), with a treatment capacity of 5000mL / batch. After adsorption treatment, the average concentration of effluent ammonia nitrogen dropped to 0.74mg / L, meeting the requirements of relevant regional sewage discharge standards such as the Pollutant Discharge Standard for Urban Sewage Treatment Plants (DB32 / 4440-2022) and the Water Pollutant Discharge Standard for Urban Sewage Treatment Plants (DB11 / 890-2012).
[0039] When the adsorbed water reaches the breakthrough point, 10 mL of KCl solution with a concentration of 2 mol / L is passed through the adsorption column from top to bottom at a flow rate of 2.5 mL / h (the hydraulic retention time is 120 min) to desorb the FePO4 composite nanomaterial, and then the composite nanomaterial is rinsed with 30 mL of deionized water; the high-concentration desorption liquid is used for ammonia nitrogen recovery, and the low-concentration desorption liquid is returned to the desorption liquid pool for preparing the KCl solution; after desorption, the FePO4 composite nanomaterial can be reused for treating sewage with excessive ammonia nitrogen. After 10 cycles of adsorption-desorption operations, the average ammonia nitrogen concentration of the effluent after treating the above wastewater with the FePO4 composite nanomaterial drops to 0.78 mg / L, and the effective treatment capacity is 4700 mL / batch.
[0040] Example 2
[0041] The preparation method of the FePO4 composite nanomaterial of the present invention comprises the following steps:
[0042] (1) Fe(NO3)3·9H2O is fully dissolved in an aqueous solution containing 7.5% (V / V) ethanol, the concentration of Fe(NO3)3·9H2O is controlled to be 0.35 mol / L, and the pH of the solution is adjusted with HNO3 to be ≤ 1.0; sulfonated polystyrene microspheres are added to the above mixed solution, the dosage of the polystyrene microspheres is 150 g / L, and the mixture is stirred and reacted at 20 °C for 12 h to obtain polystyrene microspheres pre-loaded with Fe(III).
[0043] (2) The above polystyrene microspheres pre-loaded with Fe(III) are filtered out and slowly added to a phosphoric acid solution with a concentration of 0.35 mol / L, and the mixture is stirred and reacted at 65 °C for 4.5 h, and the dosage of the polystyrene microspheres pre-loaded with Fe(III) is 150 g / L; 1 mol / L NaOH and 1 mol / L HNO3 solutions are used to control the pH of the reaction system to be maintained within the range of 2 ± 0.2.
[0044] (3) The reacted polystyrene microspheres are filtered out, first rinsed thoroughly with 1 mol / L KCl solution, then washed with deionized water until the conductivity of the effluent is < 50 μS / cm, and finally infiltrated with absolute ethanol and placed in a vacuum drying oven, and vacuum dried at 80 °C for 12 h to obtain the FePO4 composite nanomaterial.
[0045] The particle size of the composite nanomaterial prepared in Example 2 is 0.5 - 1.2 mm, the pore size distribution is 5 - 20 nm, and the particle size of the FePO4 nanoparticles loaded in the pores is 10 - 40 nm; in the composite nanomaterial, the content of FePO4 is 7 wt.% (calculated by the mass percentage of Fe).
[0046] The wastewater with excessive ammonia nitrogen (ammonia nitrogen concentration is 13.6 mg / L, pH is 7.2) is introduced into a precision filter. The filter uses a polypropylene hot-sprayed fiber membrane filter element with a filtration accuracy of 1μm, a filtration pressure of 0.4MPa, an outlet turbidity of ≤0.1NTU, and a sludge density index SDI≤5.
[0047] 10mL of the FePO4 composite nanomaterial prepared in Example 2 was loaded into an adsorption column (16×160mm), and the filtrate was passed from top to bottom through the composite nanomaterial adsorption bed at a flow rate of 60mL / h (hydraulic retention time of 10min), with a treatment capacity of 7000mL / batch. After adsorption treatment, the average concentration of effluent ammonia nitrogen dropped to 0.82mg / L, meeting the requirements of relevant regional sewage discharge standards such as the Pollutant Discharge Standard for Urban Sewage Treatment Plants (DB32 / 4440-2022) and the Water Pollutant Discharge Standard for Urban Sewage Treatment Plants (DB11 / 890-2012).
[0048] When the adsorbed water reaches the breakthrough point, 20 mL of 1.5 mol / L KCl solution is used to desorb the FePO4 composite nanomaterial from top to bottom through the adsorption tower at a flow rate of 7.0 mL / h (hydraulic retention time is 85 min), and then the composite nanomaterial is rinsed with 60 mL of deionized water; the high-concentration desorption liquid is used for ammonia nitrogen recovery, and the low-concentration desorption liquid is returned to the desorption liquid pool for the preparation of KCl solution. After desorption, the FePO4 composite nanomaterial can be reused for wastewater treatment with excessive ammonia nitrogen. After 10 cycles of adsorption-desorption operation, the average ammonia nitrogen concentration of the effluent treated by the FePO4 composite nanomaterial for the above wastewater was reduced to 0.87 mg / L, and the effective treatment capacity was 6650 mL / batch.
[0049] Example 3
[0050] The preparation method of the FePO4 composite nanomaterial of the present invention comprises the following steps:
[0051] (1) Fe(NO3)3·9H2O was fully dissolved in an aqueous solution containing 10% (V / V) ethanol, the concentration of Fe(NO3)3·9H2O was controlled to be 0.5 mol / L, and the pH of the solution was adjusted to ≤1.0 with HNO3; sulfonic acid polystyrene microspheres were added to the mixed solution, the dosage of polystyrene microspheres was 200 g / L, and the reaction was stirred at 25°C for 12 h to obtain polystyrene microspheres preloaded with Fe(III);
[0052] (2) Filter out the above-mentioned polystyrene microspheres pre-loaded with Fe(III), slowly add them to a phosphoric acid solution with a concentration of 0.5 mol / L, and stir and react at 60 °C for 6 h. The dosage of the polystyrene microspheres pre-loaded with Fe(III) is 200 g / L; use 1 mol / L NaOH and 1 mol / L HNO3 solutions to control the pH of the reaction system to be within the range of 2 ± 0.2;
[0053] (3) Filter out the reacted polystyrene microspheres, first rinse them thoroughly with 1 mol / L KCl solution, then wash them with deionized water until the conductivity of the effluent is < 50 μS / cm, and finally soak them with absolute ethanol and place them in a vacuum drying oven, and vacuum dry at 80 °C for 12 h to obtain the FePO4 composite nanomaterial.
[0054] The particle size of the composite nanomaterial prepared in Example 3 is 0.5 - 1.2 mm, the pore size distribution is 5 - 20 nm, and the particle size of the FePO4 nanoparticles loaded in the pores is 10 - 40 nm; in the composite nanomaterial, the content of FePO4 is 10 wt.% (calculated by the mass percentage of Fe).
[0055] Introduce a sewage with excessive ammonia nitrogen (ammonia nitrogen concentration is 19.2 mg / L, pH is 6.7) into a precision filter. The filter uses a polypropylene hot spray fiber membrane filter element, the filtration accuracy is 1 μm, the filtration pressure is 0.4 MPa, the effluent turbidity ≤ 0.1 NTU, and the sludge density index SDI ≤ 5.
[0056] Load 50 mL of the above-prepared FePO4 composite nanomaterial into an adsorption column (32 × 260 mm), and pass the filtrate through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 250 mL / h (the hydraulic retention time is 12 min), and the treatment capacity is 25000 mL / batch. After adsorption treatment, the average ammonia nitrogen concentration of the effluent drops to 0.89 mg / L, meeting the requirements of relevant regional sewage discharge standards such as "Discharge Standards for Pollutants from Municipal Wastewater Treatment Plants (DB32 / 4440 - 2022)" and "Discharge Standards for Water Pollutants from Municipal Wastewater Treatment Plants (DB11 / 890 - 2012)".
[0057] When the adsorbed effluent reaches the breakthrough point, 100 mL of KCl solution with a concentration of 2 mol / L is passed through the adsorption column from top to bottom at a flow rate of 25 mL / h (hydraulic retention time is 120 min) to desorb the FePO4 composite nanomaterial, and then 300 mL of deionized water is used to wash the composite nanomaterial; the high-concentration desorbing solution is used for ammonia nitrogen recovery, and the low-concentration desorbing solution is returned to the desorbing solution tank for preparing KCl solution. After desorption, the FePO4 composite nanomaterial can be reused for treating sewage with excessive ammonia nitrogen. After 10 cycles of adsorption-desorption operation, the average ammonia nitrogen concentration of the effluent after treating the above wastewater by the FePO4 composite nanomaterial drops to 0.92 mg / L, and the effective treatment capacity is 23700 mL / batch.
[0058] Comparative Example 1
[0059] The preparation method of the composite nanomaterial in Comparative Example 1 is basically the same as that in Example 2, the only difference being that in step (1), HNO3 is not used to adjust the solution pH ≤ 1.0, and the Fe(OH)3 composite nanomaterial is prepared.
[0060] A certain sewage with excessive ammonia nitrogen (ammonia nitrogen concentration is 13.6 mg / L, pH is 7.2) is introduced into a precision filter. The filter uses a polypropylene hot spray fiber membrane filter element, the filtration accuracy is 1 μm, the filtration pressure is 0.4 MPa, the effluent turbidity ≤ 0.1 NTU, and the sludge density index SDI ≤ 5.
[0061] 10 mL of the Fe(OH)3 composite nanomaterial prepared in Comparative Example 1 is loaded into an adsorption column (16×160 mm), and the filtrate is passed through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 60 mL / h (hydraulic retention time is 10 min), and the treatment capacity is 7000 mL / batch. After adsorption treatment, the average ammonia nitrogen concentration of the effluent is 6.7 mg / L, which cannot meet the requirements of relevant regional sewage discharge standards such as "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (DB32 / 4440 - 2022)" and "Discharge Standard of Water Pollutants for Municipal Wastewater Treatment Plants (DB11 / 890 - 2012)".
[0062] Since HNO3 was not added in step (1) to adjust the solution pH ≤ 1.0, Fe(NO3)3·9H2O will undergo hydrolysis reaction in an aqueous solution containing 7.5% (V / V) ethanol to generate Fe(OH)3, making it impossible for the iron precursor to be pre-loaded in the pores of sulfonated polystyrene microspheres in the form of Fe(III) ions through ion exchange, and only precipitating on the surface of polystyrene microspheres in the form of Fe(OH)3; and after adding phosphoric acid solution subsequently, FePO4 cannot be generated by reaction either. On the one hand, the amount of Fe(OH)3 precipitated on the surface of polystyrene microspheres is small. On the other hand, Fe(OH)3 cannot achieve selective adsorption of ammonia nitrogen in sewage through the combined action of hydrogen bonding, electrostatic attraction and chemical precipitation, ultimately resulting in a significant decline in the adsorption performance of ammonia nitrogen.
[0063] Comparative Example 2
[0064] The preparation method of the composite nanomaterial in Comparative Example 2 is basically the same as that in Example 2, and the only difference is that HCl is used in step (1) to adjust the solution pH ≤ 1.0 to prepare the FePO4 composite nanomaterial.
[0065] A certain sewage with excessive ammonia nitrogen (ammonia nitrogen concentration is 13.6 mg / L, pH is 7.2) is introduced into a precision filter. The filter uses a polypropylene hot spray fiber membrane filter element, with a filtration accuracy of 1 μm, a filtration pressure of 0.4 MPa, an effluent turbidity ≤ 0.1 NTU, and a sludge density index SDI ≤ 5.
[0066] 10 mL of the FePO4 composite nanomaterial prepared in Comparative Example 2 is loaded into an adsorption column (16 × 160 mm), and the filtrate is passed through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 60 mL / h (the hydraulic retention time is 10 min), and the treatment capacity is 7000 mL / batch. After adsorption treatment, the average ammonia nitrogen concentration of the effluent is 7.5 mg / L, which cannot meet the requirements of relevant regional sewage discharge standards such as "Discharge Standards for Pollutants from Municipal Wastewater Treatment Plants (DB32 / 4440 - 2022)" and "Discharge Standards for Water Pollutants from Municipal Wastewater Treatment Plants (DB11 / 890 - 2012)".
[0067] Since HCl is used to adjust the solution pH in step (1), Cl - and Fe 3+ can form a stable complex [FeCl4] - , significantly reducing the concentration of free Fe 3+ in the solution; [FeCl4] -The complex ion is negatively charged and has an electrostatic repulsion with the sulfonic acid group - modified polystyrene microspheres, and cannot be pre - loaded into the polystyrene pores through ion - exchange, resulting in a significant reduction in the pre - loading amount of Fe(III) in the polystyrene pores in step (1). This leads to a substantial decrease in the amount of FePO4 formed by in - situ precipitation of phosphoric acid subsequently, and ultimately results in a significant decline in the ammonia - nitrogen adsorption performance.
[0068] Comparative Example 3
[0069] The preparation method of the composite nanomaterial in Comparative Example 3 is basically the same as that in Example 2, with the only difference being that the pH of the reaction system was not controlled to be within the range of 2±0.2 in step (2), and a HFO (hydrated iron oxide) composite nanomaterial was prepared.
[0070] A sewage with excessive ammonia - nitrogen (ammonia - nitrogen concentration is 13.6 mg / L, pH is 7.2) is introduced into a precision filter. The filter uses a polypropylene hot - sprayed fiber membrane filter element, with a filtration accuracy of 1 μm, a filtration pressure of 0.4 MPa, an effluent turbidity ≤0.1 NTU, and a sludge density index SDI ≤5.
[0071] 10 mL of the HFO composite nanomaterial prepared in Comparative Example 3 is loaded into an adsorption column (16×160 mm), and the filtrate is passed through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 60 mL / h (hydraulic retention time is 10 min), and the treatment capacity is 7000 mL / batch. After adsorption treatment, the average ammonia - nitrogen concentration of the effluent is 6.1 mg / L, which cannot meet the requirements of relevant regional sewage discharge standards such as "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (DB32 / 4440 - 2022)" and "Discharge Standard of Water Pollutants for Municipal Wastewater Treatment Plants (DB11 / 890 - 2012)".
[0072] Since the pH of the reaction system was not controlled to be within the range of 2±0.2 in step (2), at the initial stage of the reaction, the pH of the phosphoric acid solution was relatively low (<1.5). At this time, the reaction product of the pre - loaded Fe(III) ions in the polystyrene microspheres and phosphoric acid was mainly Fe(H2PO4)3. As the reaction time continued, phosphoric acid was consumed and the reaction product HNO3 (HNO3 was used to adjust the pH of the reaction solution to 2±0.2 initially, and NaOH or HNO3 should be supplemented according to the change of the pH of the reaction system during the reaction. If not supplemented, HNO3 was gradually consumed) gradually volatilized under the heating condition of 60°C, resulting in an increase in the solution pH. The pre - loaded Fe(III) ions in the polystyrene microsphere pores would hydrolyze to form hydrated iron oxide (HFO), and finally a HFO composite nanomaterial was prepared. The HFO loaded in the composite nanomaterial could not achieve the selective adsorption of ammonia - nitrogen in sewage through the combined action of hydrogen bonding, electrostatic attraction, and chemical precipitation, ultimately leading to a significant decline in the ammonia - nitrogen adsorption performance.
[0073] Comparative Example 4
[0074] The preparation method of the composite nanomaterial in Comparative Example 4 was basically the same as that in Example 2, and the only difference was that in step (2), the stirring reaction was carried out at 85 °C for 4.5 h to prepare the Fe(OH)3 composite nanomaterial.
[0075] A certain sewage with excessive ammonia nitrogen (ammonia nitrogen concentration of 13.6 mg / L, pH of 7.2) was introduced into a precision filter. The filter used a polypropylene hot-spray fiber membrane filter element with a filtration accuracy of 1 μm, a filtration pressure of 0.4 MPa, an effluent turbidity ≤ 0.1 NTU, and a sludge density index SDI ≤ 5.
[0076] 10 mL of the Fe(OH)3 composite nanomaterial prepared in Comparative Example 4 was loaded into an adsorption column (16×160 mm), and the filtrate was passed through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 60 mL / h (hydraulic retention time was 10 min), and the treatment capacity was 7000 mL / batch. After adsorption treatment, the average ammonia nitrogen concentration of the effluent was 6.5 mg / L, which could not meet the requirements of relevant regional sewage discharge standards such as "Discharge Standards for Pollutants from Municipal Wastewater Treatment Plants (DB32 / 4440-2022)" and "Discharge Standards for Water Pollutants from Municipal Wastewater Treatment Plants (DB11 / 890-2012)".
[0077] Since the temperature of the stirring reaction in step (2) was increased to 85 °C, too high a temperature would accelerate the hydrolysis of Fe 3+ such that the pre-loaded Fe(III) hydrolyzed to form Fe(OH)3 in the pores of the polystyrene microspheres. And Fe(OH)3 could not achieve the selective adsorption of ammonia nitrogen in sewage through the combined action of hydrogen bonding, electrostatic attraction, and chemical precipitation, ultimately resulting in a significant decrease in the adsorption performance of ammonia nitrogen.
[0078] Comparative Example 5
[0079] The preparation method of the composite nanomaterial in Comparative Example 5 was basically the same as that in Example 2, and the only difference was that in step (2), polystyrene microspheres pre-loaded with Fe(III) were added to 0.5 mol / L phosphoric acid solution, and the dosage of the polystyrene microspheres pre-loaded with Fe(III) was 150 g / L to prepare the Fe2(HPO4)3 (ferric hydrogen phosphate) composite nanomaterial.
[0080] A certain sewage with excessive ammonia nitrogen (ammonia nitrogen concentration of 13.6 mg / L, pH of 7.2) was introduced into a precision filter. The filter used a polypropylene hot-spray fiber membrane filter element with a filtration accuracy of 1 μm, a filtration pressure of 0.4 MPa, an effluent turbidity ≤ 0.1 NTU, and a sludge density index SDI ≤ 5.
[0081] Load 10 mL of the Fe(OH)3 composite nanomaterial prepared in Comparative Example 5 into an adsorption column (16×160 mm), and pass the filtrate through the composite nanomaterial adsorption bed layer from top to bottom at a flow rate of 60 mL / h (hydraulic retention time is 10 min), with a treatment capacity of 7000 mL / batch. After adsorption treatment, the average concentration of ammonia nitrogen in the effluent is 4.5 mg / L, which cannot meet the requirements of relevant regional sewage discharge standards such as "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (DB32 / 4440-2022)" and "Discharge Standard of Water Pollutants for Municipal Wastewater Treatment Plants (DB11 / 890-2012)".
[0082] Since the concentration of the phosphoric acid solution in step (2) is 0.5 mol / L, compared with the pre-loaded Fe(III), the phosphoric acid is in excess. Under acidic conditions, HPO4 2- is formed, causing the pre-loaded Fe(III) to generate ferric hydrogen phosphate Fe2(HPO4)3 in the pores of the polystyrene microspheres. However, Fe2(HPO4)3 cannot achieve selective adsorption of ammonia nitrogen in sewage through hydrogen bonding, electrostatic attraction, chemical precipitation and other effects, ultimately resulting in a significant decline in the adsorption performance of ammonia nitrogen.
[0083] Figure 2 It shows that Fe and P elements are evenly distributed on the cross-section of the composite nanomaterial, indicating that FePO4 has been evenly loaded inside the pores of the sulfonic acid group polystyrene carrier; Figure 3 It shows that the particle size of the FePO4 nanoparticles loaded in the pores of the composite nanomaterial is 10 - 40 nm. By Figure 4 it can be known that the FePO4 composite nanomaterial of the present invention has strong stability and can be used stably for a long time under the condition of pH 3 - 10, and the loaded FePO4 nanoparticles do not dissolve out.
Claims
1. A FePO4 composite nanomaterial for removing ammonia nitrogen in sewage, characterized in that: The composite nanomaterial uses sulfonic acid group-modified polystyrene microspheres as carriers, and FePO4 nanoparticles are immobilized in the pores of the polystyrene microspheres.
2. The FePO4 composite nanomaterial according to claim 1, characterized in that: The particle size of the composite nanomaterial is 0.5 - 1.2 mm, and the particle size of the FePO4 nanoparticles immobilized in the pores of the polystyrene microspheres is 10 - 40 nm; in the composite nanomaterial, the content of FePO4 is 4 - 10 wt.% in terms of the mass percentage of Fe.
3. The preparation method of the FePO4 composite nanomaterial according to claim 1, characterized in that, It includes the following steps: (1) Dissolve Fe(NO3)3·9H2O in an aqueous solution of ethanol to obtain a mixed solution, and adjust the pH of the solution to ≤ 1.0 with HNO3. (2) Add the sulfonic acid group-modified polystyrene microspheres to the mixed solution in step (1), and after reaction, obtain polystyrene microspheres pre-loaded with Fe(III). (3) Slowly add the polystyrene microspheres pre-loaded with Fe(III) in step (2) to the phosphoric acid solution, stir and react at 60 - 70 °C for 3 - 6 h, and control the pH of the reaction system during the reaction to be maintained within the range of 2 ± 0.
2. (4) Filter out the polystyrene microspheres after the reaction in step (3), wash them thoroughly and dry them to obtain the FePO4 composite nanomaterial.
4. The preparation method according to claim 3, characterized in that: In step (1), in the aqueous solution of ethanol, the volume of ethanol accounts for 5 - 10% of the total volume of the solution.
5. The preparation method according to claim 3, characterized in that: In steps (1) - (2), in the mixed solution, the addition concentration of Fe(NO3)3·9H2O is 0.2 - 0.5 mol / L, and the dosage of the polystyrene microspheres is 100 - 200 g / L.
6. The preparation method according to claim 3, wherein: In step (2), the reaction temperature is 15 - 25 °C, and the reaction time is not less than 12 h.
7. The preparation method according to claim 3, wherein: In step (3), the concentration of the phosphoric acid solution is 0.2 - 0.5 mol / L; in the phosphoric acid solution, the dosage of the polystyrene microspheres pre-loaded with Fe(III) is 100 - 200 g / L.
8. The preparation method according to claim 3, characterized in that: In step (3), use NaOH and HNO3 solutions to control the pH of the reaction system during the reaction to be 2 ± 0.
2.
9. The preparation method according to claim 3, wherein: In step (3), during the reaction process, the reaction system is kept in a stirred state, and the stirring speed is ≥ 600 rpm.
10. The preparation method according to claim 3, characterized in that: In step (4), first rinse thoroughly with a 1 mol / L KCl solution, then wash with deionized water until the conductivity of the effluent water < 50 μS / cm, and finally infiltrate with absolute ethanol and place it in a vacuum drying oven, and vacuum dry at 80 - 85 °C for 10 - 12 h.