A method for targeted deep treatment of nitrate in water

Abstract

This invention discloses a method for targeted deep treatment of nitrate in water. The method includes: adjusting the pH of the nitrate-containing water and then filtering it; passing the resulting filtrate through an adsorption tower or fluidized bed filled with ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material to obtain treated water; and regenerating the water by reduction with sodium borohydride solution when a leak point is reached. This invention utilizes ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material to treat nitrate. It has been found that even when the water pH is between 3.0 and 11.0, and high concentrations of inorganic anions such as chloride, bicarbonate, and sulfate are present, the nitrate content in the effluent is reduced from less than 200 mg / L (as N) to below 0.01 mg / L. Simultaneously, the selectivity of nitrogen gas, the nitrate reduction product, is greater than 95%, and the material can be reused.

Description

Technical Field

[0001] This invention relates to the field of advanced wastewater treatment and harmless treatment technology, and in particular to a method for targeted advanced treatment of nitrates in water. Background Technology

[0002] Nitrate is part of the nitrogen cycle. Among various forms of nitrogen compounds, nitrate is the most stable. Large amounts of nitrate nitrogen in groundwater mainly originate from domestic sewage and excrement, fertilizers, industrial wastewater, atmospheric nitrogen oxide deposition (both dry and wet), and wastewater irrigation. It is generally believed that excessive application of nitrogen fertilizer is the primary cause of nitrate pollution in groundwater. Since the artificial synthesis of nitrogen fertilizers at the beginning of the last century, the significant increase in global crop yields per unit area has largely depended on the continuous increase in nitrogen fertilizer application. Although nitrogen fertilizer application in farmland increases grain yield by at least 40%, due to differences in crop types and fertilization techniques, only 25-85% of the applied nitrogen fertilizer is absorbed and utilized by plants. Most nitrogen fertilizer enters the environment through various pathways, especially runoff and leaching losses from farmland, resulting in excessively high nitrate levels in many surface and groundwater sources. Domestic sewage and excrement from residential areas are a significant source of groundwater pollution. Large quantities of sewage and excrement seep into the ground through infiltration wells and septic tanks. The organic nitrogen compounds in these substances decompose under the action of soil microorganisms, producing amino acids that are then ammonified to synthesize ammonia. These ammonia is then converted to nitrite by nitrite-forming bacteria, and finally oxidized to nitrate by nitrifying bacteria, resulting in nitrate pollution in groundwater. Modern industrial development, particularly in light industries such as food processing, leather manufacturing, and papermaking, discharges wastewater containing large amounts of organic matter. This organic wastewater can seep into groundwater and be converted into nitrates, providing the necessary conditions for nitrate formation. Furthermore, the combustion of coal, oil, natural gas, and plant matter also produces large amounts of nitrogen oxides. These nitrogen oxides, through chemical reactions, form nitrates that settle or are carried by rainwater to the surface, soil, rivers, and lakes, ultimately also entering the groundwater. In recent years, with the increasing scarcity of water resources, sewage irrigation has increased and the area of ​​sewage irrigation has expanded significantly. Although sewage irrigation can alleviate the contradiction between agricultural water use and water shortage to a certain extent, sewage contains a large amount of organic nitrogen compounds. If irrigation is not carried out properly, these compounds will not only pollute the farmland environment and directly harm the soil and crops, but also pollute groundwater with the participation of soil microorganisms, leading to an increase in nitrates in groundwater.

[0003] For the natural environment, excessive nitrate levels in surface water can cause eutrophication, leading to excessive growth of algae and aquatic plants and severe degradation of aquatic ecosystems. Algae also consume dissolved oxygen during their growth, creating an oxygen-deficient environment, causing the death of plants and animals in natural aquatic bodies and disrupting the aquatic ecological balance. For humans, nitrates themselves are not particularly harmful; excessive levels may cause diarrhea and intestinal dysfunction, but they do not cause serious harm. The main danger of nitrates lies in their ability to be converted into nitrites in the body by nitrate reductase. Nitrites, under the influence of various nitrogen-containing organic compounds such as ammonium urea and cyanamide, can be transformed into nitrosamines and nitrosamides, which are carcinogenic, teratogenic, and mutagenic, inducing various tumors in the human body, such as tumors of the intestines, nervous system, brain, skin, and bones. Currently, my country's Drinking Water Hygiene Standard (GB5749-2006) stipulates that the limit for nitrates (calculated as N) in drinking water is 10 mg / L.

[0004] In recent years, various technologies have been employed to remove nitrates from wastewater, such as catalytic hydrogenation reduction, NZVI reduction, biological denitrification, and ion exchange. Catalytic hydrogenation reduction requires hydrogen as a reducing agent, posing certain safety risks, and hydrogen has low solubility in water, resulting in low utilization. NZVI reduction exhibits low nitrogen selectivity, and the reduction product is primarily ammonia nitrogen. Biological denitrification requires an external carbon source (methanol, ethanol, acetic acid, etc.), causing secondary pollution. While autotrophic microorganisms do not require a carbon source, their slow growth and low removal efficiency contribute to the problem. Ion exchange lacks selectivity for nitrates; it merely adsorbs and transfers nitrate ions without eliminating their harmful effects.

[0005] Therefore, converting nitrates into harmless nitrogen gas via a redox method is the optimal treatment solution. However, ammonia nitrogen is produced as a byproduct during the reaction, thus requiring materials with good directional reduction properties to convert nitrate ions into nitrogen gas in a specific direction.

[0006] Currently, literature searches indicate that there are no reports of methods for the directional reduction of nitrate in water using ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposites. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a method for the targeted reduction of nitrate in water using an ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite material. This method overcomes the shortcomings of traditional nanocomposite materials, which can only simply adsorb or reduce nitrate primarily to ammonia nitrogen. Furthermore, the reacted ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite material can be regenerated with sodium borohydride solution and reused. By loading the nano-zero-valent palladium-tin bimetallic material onto a resin carrier, the method ensures the targeted reduction of nitrate in water while avoiding the risk of secondary pollution caused by the leaching of nano-metal particles into the water.

[0008] The specific technical solution is as follows:

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for the directional reduction of nitrate in water using ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials, comprising the following steps:

[0010] (1) Adjust the pH of the water containing nitrate, filter it, and obtain the filtrate;

[0011] (2) The filtrate obtained in step (1) is passed through an adsorption tower or fluidized bed filled with ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material, so that the nitrate-containing water and the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material are in full contact to obtain the treated water.

[0012] The ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material uses chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules as the matrix. The copolymer spheres have uniformly distributed nanopores, and zero-valent palladium and zero-valent tin bimetallic nanoparticles are uniformly distributed in the pores.

[0013] (3) When the treated water reaches the leak point, stop the operation and use sodium borohydride solution for reduction to achieve the regeneration of zero-valent palladium and zero-valent tin.

[0014] The ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material used in this invention is based on grafting ethylenediamine (NH2CH2CH2NH2) groups onto the framework of chloromethylated polystyrene copolymer spheres and loading nano-sized zero-valent palladium-tin bimetallic particles. Metallic tin can first reduce nitrate ions in water to nitrite ions, and metallic palladium has active chemical properties and good acid and alkali resistance. Simultaneously, the adsorbed hydrogen generated on its surface has good reducing ability, selectively reducing most of the generated nitrite ions to nitrogen gas.

[0015] Further, in step (1), the pH value is 3.0 to 11.0, preferably pH 5; the mass concentration of nitrate in the water is less than 200 mg / L (calculated as N), and the mass concentration of other coexisting anions in the water is less than 500 times the mass concentration of nitrate ions.

[0016] Furthermore, in step (2), the temperature of the filtrate passing through the ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite material is 5 to 40°C, and the flow rate of the filtrate is less than or equal to 30 resin bed volumes per hour.

[0017] Further, in step (3), the leakage point is where the mass concentration of nitrate in the effluent is >0.01 mg / L (calculated as N).

[0018] Further, in step (3), the sodium borohydride solution is an aqueous solution of sodium borohydride with a mass percentage concentration of 0.5-5%; when the sodium borohydride solution passes through the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material, it is regenerated at a flow rate of 1-5 resin bed volumes per hour at 15-60°C.

[0019] Furthermore, steps (2) and (3) employ a single-tower adsorption-desorption or multi-tower series adsorption-single-tower desorption operation mode.

[0020] Furthermore, the palladium loading in the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material is 4-14% (mass fraction), and the tin loading is 0.6-2% (mass fraction).

[0021] Furthermore, the preparation method of the ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite material includes the following steps:

[0022] 1) Chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules are ethylenediamine resin. After washing them with ethanol in a Soxhlet extractor, they are dried in a constant temperature oven to obtain pretreated ethylenediamine resin.

[0023] 2) The pretreated ethylenediamine resin was immersed in a hydrochloric acid solution containing palladium and tin salts. After thorough impregnation, it was filtered to obtain Pd-loaded resin. 2+ and Sn 4+ Ethylenediamine resin of the complex;

[0024] 3) To load Pd 2+ and Sn 4+ A 0.2–1.0% sodium borohydride solution was added dropwise to the ethylenediamine resin of the complex to carry out a reduction reaction, thereby reducing Pd. 2+ and Sn 4+ The complex was reduced to zero-valent metallic Pd-Sn, and then subjected to solid-liquid separation and washing to obtain an ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material.

[0025] Furthermore, the preparation method of the chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules in step 1) is as follows:

[0026] (a) Chloromethylated polystyrene resin was added to dimethylformamide (DMF) swelling agent for swelling treatment;

[0027] (b) Filter out the swelling agent, separate the swollen chloromethylated polystyrene resin, add it to a mixed solution of ethylenediamine and ethanol, carry out the grafting reaction under water bath conditions, filter out the mixed solution, and obtain the grafted chloromethylated polystyrene resin.

[0028] (c) Wash the grafted chloromethylated polystyrene resin with distilled water, then remove impurities from the chloromethylated polystyrene resin by Soxhlet extraction with ethanol, and dry it under vacuum at room temperature to complete the preparation.

[0029] Furthermore, in step (a), the swelling treatment time is 12-4 hours; in step (b), the volume ratio of ethylenediamine to ethanol in the mixed solution is 1:1-3, preferably 1:2; the mass-volume ratio of the chloromethylated polystyrene resin to the mixed solution is 1 g: 20-30 mL; in step (b), the grafting reaction temperature is 55-65°C, and the reaction time is 20-30 hours.

[0030] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0031] 1) The method of this invention utilizes ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material to treat nitrate. It was found that when the pH of the water body is 3.0 to 11.0 and there are high concentrations of inorganic anions such as chloride ions, bicarbonate ions, and sulfate ions, the nitrate content in the effluent is still reduced from less than 200 mg / L (calculated as N) to less than 0.01 mg / L. At the same time, the selectivity of nitrogen gas, the nitrate reduction product, is greater than 95%, and the material can be reused after regeneration.

[0032] 2) The method of the present invention uses ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material to treat nitrate ions. The material used has good directional reduction performance for nitrate ions, directionally converting nitrate ions into nitrogen gas, with virtually no byproduct ammonia nitrogen generated.

[0033] 3) Through extensive creative experiments, the applicant discovered that the ethylenediamine resin modified with chloromethylated polystyrene copolymer spheres, in synergy with the zero-valent palladium-tin bimetallic active component, has a very good technical effect in the targeted removal of nitrates. Attached Figure Description

[0034] Figure 1 TEM image of the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite obtained in blank example 1;

[0035] Figure 2 The results show the effect of different pH values ​​on the removal performance of nitrate ions in water in Examples 2-6. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0037] Chloromethylated polystyrene copolymer spheres are a conventional material. They are produced by chloromethylating white spheres (styrene-divinylbenzene copolymer) with chloromethyl ether in the presence of a catalyst (such as anhydrous ZnCl2), introducing the -CH2Cl active group to obtain the chloromethylated polystyrene copolymer spheres. In this embodiment of the invention, the chloromethylated polystyrene resin was purchased directly from Ningbo Zhengguang Resin Co., Ltd., eliminating the need for manual chloromethylation.

[0038] Blank example 1:

[0039] The ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material involved in the following examples is prepared by the following method:

[0040] 1) A certain amount of chloromethylated polystyrene resin was added to dimethylformamide (DMF) swelling agent and swollen for 12 hours;

[0041] 2) Filter out the swelling agent, separate the swollen chloromethylated polystyrene resin, add it to a mixed solution of ethylenediamine and ethanol (volume ratio of ethylenediamine and ethanol is 1:2) (mass-volume ratio of chloromethylated polystyrene resin to mixed solution is 1g:30mL), carry out the grafting reaction in a 65℃ water bath for 24 hours, filter out the mixed solution, and obtain the grafted chloromethylated polystyrene resin;

[0042] 3) Wash the grafted chloromethylated polystyrene resin with distilled water, then remove impurities from the chloromethylated polystyrene resin by Soxhlet extraction with ethanol, and vacuum dry at room temperature to obtain ethylenediamine resin;

[0043] 4) Prepare the precursor solution. The molar concentrations of palladium chloride and tin tetrachloride pentahydrate in the precursor solution are 2.26 mM and 6.84 mM, respectively, and the concentration of hydrochloric acid is 0.5 mol / L. Take 0.2 g of the ethylenediamine resin from step 3) and soak it in 100 ml of the prepared precursor solution. Then place it in a constant temperature shaker and shake at 25°C and 180 rpm for 18 h.

[0044] 5) Filter out the precursor solution and separate the loaded Pd. 2+ and Sn 4+- The ethylenediamine resin of the complex was then added dropwise with a 5% sodium borohydride solution, followed by ultrasonic reduction for 35 minutes to reduce Pd. 2+and Sn 4+ The complex is reduced to zero-valent metallic Pd-Sn;

[0045] 6) After ultrasonic treatment, solid-liquid separation was performed to obtain ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials. After washing with ethanol and then with ultrapure water, the filtered resin was dried under vacuum at 60°C to obtain the ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials. A TEM image of the ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials obtained in Blank Example 1 is shown below. Figure 1 As shown.

[0046] After digesting the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite obtained in blank example 1 with aqua regia, ICP analysis revealed that the Pd loading in the composite was 7.16% (mass fraction) and the Sn loading was 0.96% (mass fraction). The amount of tin tetrachloride pentahydrate used in the preparation of the composite was significantly higher than that of palladium chloride; however, the Pd loading in the composite was significantly higher than that of Sn. This may be because the ethylenediamine resin preferentially coordinates with Pd before binding with Sn. After the ethylenediamine resin coordinates with Pd, the number of active sites is greatly reduced, resulting in a lower final Sn content.

[0047] Example 1

[0048] A method for the targeted reduction of nitrate in water using ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials, with the following specific steps:

[0049] (1) 0.2g of ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material was placed in a solution containing nitrate; the concentration of nitrate was 2mmol / L, i.e. 28mg / L (as N), the volume of the solution was 50mL, the pH of the solution was adjusted to 6±0.2, and the solution was placed in a constant temperature shaker and shaken for 24h to carry out adsorption and directional reduction reactions.

[0050] (2) After the reaction was completed, the supernatant of the solution after the directional reduction reaction was taken and the concentrations of nitrate, nitrite and ammonia nitrogen were measured. The results showed that the concentration of nitrate after the reaction was 5.1±0.5mg / L (calculated as N), and nitrite and ammonia nitrogen were basically undetectable.

[0051] (3) After separating the resin from the solution, it was washed with distilled water until no nitrate ions were present in the solution. 100 mL of 0.1 mol / L sodium hydroxide solution was added for desorption. The solution was then placed in a constant temperature shaker at 25±5℃ and 180 rpm for 24 h. The supernatant was then taken, the pH was adjusted, and the concentrations of nitrate, nitrite, and ammonia nitrogen were measured. The nitrate concentration in the solution after alkaline desorption was found to be 4.0±0.3 mg / L (as N), the nitrite concentration was 0.77±0.2 mg / L (as N), and ammonia nitrogen was virtually undetectable. From (2) and (3), it can be seen that the nitrate removal rate was 82–84%, and the nitrogen selectivity was 94–95%.

[0052] (4) After the reaction, the resin was washed with distilled water until no nitrate ions were detected in the solution and the pH of the solution was neutral. After solid-liquid separation, the resin was placed in a vacuum dryer for drying. After drying, 100 ml of sodium borohydride solution (mass fraction of 0.5%) was added dropwise. After the addition was completed, the solution was sonicated for 35 min. Steps (1), (2), and (3) were repeated. The results of this experiment were basically consistent with the results of the first experiment on the material. Therefore, it was determined that the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material was completely regenerated and that the regenerated ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material could be reused.

[0053] Example 2

[0054] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 3±0.2, the nitrate removal rate was 88%, the nitrogen selectivity was 94%, and ammonia nitrogen was basically undetectable.

[0055] Example 3

[0056] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 5±0.2, the nitrate removal rate was 89%, the nitrogen selectivity was 95%, and ammonia nitrogen was basically undetectable.

[0057] Example 4

[0058] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 7±0.2, the nitrate removal rate was 83%, the nitrogen selectivity was 93%, and ammonia nitrogen was basically undetectable.

[0059] Example 5

[0060] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 9±0.2, the nitrate removal rate was 82%, the nitrogen selectivity was 93%, and ammonia nitrogen was basically undetectable.

[0061] Example 6

[0062] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 11±0.2, the nitrate removal rate was 69%, the nitrogen selectivity was 92%, and ammonia nitrogen was basically undetectable.

[0063] The results of the effect of different pH values ​​on the nitrate removal performance in Examples 2-6 are shown in the figure. Figure 2 . Figure 2 In the process, the removed nitrate ions are divided into two parts, namely the reduced NO3. - (reduced to N2 and NO2) - ) and adsorbed NO3 - .

[0064] Nitrate removal rate = (initial nitrate concentration - nitrate concentration in the solution after directional reduction) / initial nitrate concentration * 100%.

[0065] Since ammonia nitrogen was virtually undetectable in the test, the nitrate removal rate = (NO3 adsorbed by the resin) / (NO3 adsorbed by the resin). - The reduction products N2 and NO2 - The total molar amount of the three (in N) / the initial molar amount of nitrate in the water (in N) * 100%.

[0066] NO2 - Selectivity = NO2 generated by reduction - Total molar amount (in terms of N) / Molar amount of nitrate ions reduced and converted (in terms of N) * 100%.

[0067] Selectivity of ammonia nitrogen = Total molar amount of ammonia nitrogen generated by reduction (in terms of N) / Molar amount of nitrate ions converted by reduction (in terms of N) * 100%.

[0068] Therefore, the selectivity of nitrogen = 1 - NO2 - Selectivity of ammonia nitrogen = 1 - NO2 - The selectivity.

[0069] The content of nitrate ions after reduction and transformation is equal to the initial content of nitrate ions in the water body - the content of nitrate ions in the solution after directional reduction - the content of nitrate ions in the solution after alkaline desorption.

[0070] Example 7

[0071] The same method as in Example 1 was used to treat nitrate in the water, except that the temperature of the constant temperature shaker in step (3) was controlled at 15±5℃, and the nitrate removal rate and nitrogen selectivity remained basically unchanged.

[0072] Example 8

[0073] The same method as in Example 1 was used to treat nitrate in the water, except that the pH of the reaction was controlled at 25±5℃, and the nitrate removal rate and nitrogen selectivity remained basically unchanged.

[0074] Example 9

[0075] The same method as in Example 1 was used to treat nitrate in the water, except that the temperature of the constant temperature shaker in step (3) was controlled at 35±5℃, and the removal rate of nitrate and the selectivity of nitrogen remained basically unchanged.

[0076] Example 10

[0077] The same method as in Example 1 was used to treat nitrate in the water, except that the initial concentration of nitrate in step (1) was controlled at 14 mg / L, and the removal rate of nitrate and the selectivity of nitrogen were close to 100%.

[0078] Example 11

[0079] The same method as in Example 1 was used to treat nitrate in the water, except that the initial concentration of nitrate in step (1) was controlled at 56 mg / L, the nitrate removal rate decreased to 55%, and the selectivity of nitrogen remained basically unchanged.

[0080] Example 12

[0081] A method for treating nitrate in water by directionally reducing nitrate using ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials, the specific steps of which are as follows:

[0082] (1) Adjust the pH of the nitrogen-containing water (nitrate concentration of 1.4 ppm) to 6.0, filter, and obtain the filtrate;

[0083] (2) 50 mL (about 25 g) of ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material was loaded into a jacketed glass adsorption column (Φ32×360 mm). At 25±5℃, the filtrate obtained in step (1) was passed through the adsorption column containing the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material bed at a flow rate of 15 BV / h. The treatment capacity was about 9000 BV, and the concentration of nitrate in the effluent was reduced by less than 10 ppb.

[0084] (3) When the leak point is reached (the nitrate concentration in the effluent is greater than 10 ppb), stop the operation, add 1000 mL of sodium borohydride solution (sodium borohydride mass percentage concentration is 0.5%) and regenerate it by passing it through the resin bed in the same direction at a flow rate of 1 BV / h at a temperature of 25±5℃. Then clean it with ethanol. The overall regeneration rate of the composite material is >90%.

[0085] Example 13

[0086] The directional conversion of nitrate in water was carried out using the same method as in Example 12, except that in step (1), 14 ppm of SO4 was added to the nitrate-containing water. 2- (The cation is Na) + (The same applies below), and its processing effect and processing capacity remain basically unchanged.

[0087] Example 14

[0088] The directional conversion of nitrate in water was carried out using the same method as in Example 12, except that in step (1), 14 ppm of Cl was added to the nitrate-containing water. - The processing effect and processing capacity remain basically unchanged.

[0089] Example 15

[0090] The directional conversion of nitrate in water was carried out using the same method as in Example 12, except that in step (1), 14 ppm of HCO3 was added to the nitrate-containing water. - The processing effect and processing capacity remain basically unchanged.

[0091] Example 16

[0092] A method for treating nitrate in water by directionally reducing nitrate using ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite materials, the specific steps of which are as follows:

[0093] (1) Adjust the pH of the nitrogen-containing water (nitrate concentration of 140 ppm) to 6.0, filter, and obtain the filtrate;

[0094] (2) 200 mL (about 100 g) of ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material was loaded into a jacketed glass adsorption column (Φ32×360 mm). At 25±5℃, the filtrate obtained in step (1) was passed through the adsorption column containing the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material bed at a flow rate of 5 BV / h. The treatment capacity was about 150 BV, and the concentration of nitrate in the effluent was reduced by less than 10 ppb.

[0095] (3) When the leak point is reached (the nitrate concentration in the effluent is greater than 10 ppb), stop the operation, add 1000 mL of sodium borohydride solution (sodium borohydride mass percentage concentration is 0.5%) and regenerate it by passing it through the resin bed in the same direction at a flow rate of 1 BV / h at a temperature of 25±5℃. Then clean it with ethanol. The overall regeneration rate of the composite material is >90%.

[0096] Example 17

[0097] The directional conversion of nitrate in water was carried out using the same method as in Example 16, except that in step (1), 14 ppm of SO4 was added to the nitrate-containing water. 2- The processing effect and processing capacity remain basically unchanged.

[0098] Example 18

[0099] The directional conversion of nitrate in water was carried out using the same method as in Example 16, except that in step (1), 14 ppm of Cl was added to the nitrate-containing water. - The processing effect and processing capacity remain basically unchanged.

[0100] Example 19

[0101] The directional conversion of nitrate in water was carried out using the same method as in Example 16, except that in step (1), 14 ppm of HCO3 was added to the nitrate-containing water. - The processing effect and processing capacity remain basically unchanged.

[0102] Example 20

[0103] The same method as in Implementation Case 1 was used to treat nitrate in the water, except that: during the targeted reduction of nitrate in the water, the dosage of ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material was 0.05 g, 0.1 g, 0.2 g, and 0.4 g, respectively, in a 50 mL solution of nitrate with a concentration of 2 mmol / L (28 mg / L as N), and the materials were thoroughly mixed. The specific treatment results are shown in Table 1 below.

[0104] Table 1. Effect of different catalyst dosages on targeted nitrate removal.

[0105]

[0106] Example 21

[0107] The same method as in Implementation Case 1 was used to treat nitrate in the water, except that the adsorbent material was replaced by an equal mass. The specific adsorbent material selected and the corresponding experimental results are shown in Table 2.

[0108] Table 2. Effects of different materials on targeted nitrate removal.

[0109]

[0110] The preparation method of the "chlorine-based palladium-tin bimetallic composite material" in Table 2 is the same as that in Blank Example 1, except that in "step 2), the swollen chloromethylated polystyrene resin is not added to a mixed solution of ethylenediamine and ethanol (the volume ratio of ethylenediamine and ethanol is 1:2) for grafting reaction". The other conditions are the same as in Blank Example 1. The final composite material is the chlorine-based palladium-tin bimetallic composite material.

[0111] The preparation method of “D201 palladium-tin bimetallic composite material” in Table 2 is the same as that in Blank Example 1, except that in “step 4) the ethylenediamine resin is replaced with the same mass of D201 resin”. The other conditions are the same as in Blank Example 1. The final composite material is the D201 palladium-tin bimetallic composite material.

[0112] Example 22

[0113] The directional conversion of nitrate in water was carried out using the same method as in Example 1, except that in step (1), tin tetrachloride pentahydrate was replaced with copper chloride of the same molar concentration, while the other conditions remained the same as in Example 1. The final experimental results showed that the nitrate removal rate decreased to 67%, and the nitrogen selectivity decreased to 71%.

[0114] Example 23

[0115] The directional conversion of nitrate in water was carried out using the same method as in Example 1, except that the ethylenediamine resin was loaded only with palladium and not with tin, while the other conditions were the same as in Example 1. The final experimental results showed that the nitrate removal rate decreased to 70%, and the nitrogen selectivity decreased to 66%.

[0116] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for targeted and deep treatment of nitrate in water, characterized in that, Includes the following steps: (1) Adjust the pH of the nitrate-containing water body, filter, and obtain the filtrate; (2) The filtrate obtained in step (1) is passed through an adsorption tower or fluidized bed filled with ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material, so that the nitrate-containing water and the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material are in full contact to obtain the treated water. The ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material uses chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules as the matrix. The copolymer spheres have uniformly distributed nanopores, and zero-valent palladium and zero-valent tin bimetallic nanoparticles are uniformly distributed in the pores. (3) When the treated water reaches the leak point, stop the operation and then use sodium borohydride solution to reduce it to achieve the regeneration of zero-valent palladium and zero-valent tin. Then, re-enter the cycle operation of step (1)-(2). The preparation method of the ethylenediamine resin-based supported zero-valent palladium-tin bimetallic nanocomposite material includes the following steps: 1) Chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules are ethylenediamine resin. After washing them with ethanol in a Soxhlet extractor, they are dried in a constant temperature oven to obtain pretreated ethylenediamine resin. 2) The pretreated ethylenediamine resin was immersed in a hydrochloric acid solution containing palladium and tin salts. After thorough impregnation, it was filtered to obtain Pd-loaded resin. 2+ and Sn 4+ Ethylenediamine resin of the complex; 3) To load Pd 2+ and Sn 4+ A 0.2-1.0% (w / w) sodium borohydride solution was added dropwise to the ethylenediamine resin of the complex to carry out a reduction reaction, thereby reducing Pd. 2+ and Sn 4+ The complex was reduced to zero-valent metallic Pd-Sn, and then subjected to solid-liquid separation and washing to obtain an ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material. The palladium loading in the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material is 4-14% by mass, and the tin loading is 0.6-2% by mass.

2. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that, In step (1), the pH of the nitrate-containing water body is adjusted to 3.0~11.0, the mass concentration of nitrate in the water body (calculated as N) is less than 200 mg / L, and the mass concentration of other coexisting anions in the water body is less than 500 times the mass concentration of nitrate ions.

3. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that, In step (2), the adsorption temperature is 5~40℃ and the flow rate of the filtrate is less than or equal to 30 resin bed volumes per hour.

4. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that, In step (3), the leakage point is when the mass concentration of nitrate in the effluent, expressed as N, is >0.01 mg / L.

5. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that, In steps (2) and (3), a single-tower adsorption-desorption or multi-tower series adsorption-single-tower desorption operation mode is adopted.

6. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that, In step (3), the sodium borohydride solution is an aqueous solution of sodium borohydride with a mass percentage concentration of 0.5-5%; when the sodium borohydride solution passes through the ethylenediamine resin-based zero-valent palladium-tin bimetallic nanocomposite material, it is regenerated at a flow rate of 1-5 resin bed volumes per hour at 15-60°C.

7. The method for targeted deep treatment of nitrate in water as described in claim 1, characterized in that... The preparation method of the chloromethylated polystyrene copolymer spheres modified with ethylenediamine functional molecules in step 1) is as follows: (a) Chloromethylated polystyrene resin is added to dimethylformamide (DMF) swelling agent for swelling treatment; (b) Filter out the swelling agent, separate the swollen chloromethylated polystyrene resin, add it to a mixed solution of ethylenediamine and ethanol, carry out the grafting reaction under water bath conditions, filter out the mixed solution, and obtain the grafted chloromethylated polystyrene resin. (c) Wash the grafted chloromethylated polystyrene resin with distilled water, then remove impurities from the chloromethylated polystyrene resin by Soxhlet extraction with ethanol, and then vacuum dry at room temperature to complete the preparation.

8. The method for targeted deep treatment of nitrate in water as described in claim 7, characterized in that, In step (a), the swelling treatment time is 12-4 h; in step (b), the volume ratio of ethylenediamine to ethanol in the mixed solution is 1:1-3; the mass-volume ratio of chloromethylated polystyrene resin to the mixed solution is 1 g: 20-30 mL; in step (b), the grafting reaction temperature is 55-65℃ and the reaction time is 20-30 h.

9. The method for targeted deep treatment of nitrate in water as described in claim 8, characterized in that, In step (b), the volume ratio of ethylenediamine to ethanol in the mixed solution is 1:2.

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