Catalyst suitable for advanced treatment of hydrazine-containing wastewater and preparation method thereof

Abstract

The application discloses a catalyst suitable for deep treatment of hydrazine-containing wastewater and a preparation method thereof. The method uses SiO2 microspheres after etching treatment as a carrier, and the carrier is placed in a nickel-phosphorus reaction solution, nickel sulfate is used as a nickel source, sodium hypophosphite is used as a reducing agent, and palladium ions are used as a catalyst, so that redox reaction occurs at 80-95 DEG C to prepare a Ni-P-Pd@SiO2 nano catalyst. The Ni-P-Pd@SiO2 catalyst of the application can obviously improve the speed of hydrazine decomposition at normal temperature, has the characteristics of good selectivity of decomposition path, less ammonia nitrogen generation, low residual concentration of hydrazine, etc., and can be used in combination with an oxidizing agent, and is suitable for deep treatment of hydrazine-containing wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and relates to a catalyst suitable for the deep treatment of hydrazine-containing wastewater and its preparation method. Background Technology

[0002] Hydrazine and its derivatives (including hydrazine hydrate, hydrazine sulfate, hydrazine nitrate, methylhydrazine, dimethylhydrazine, phenylhydrazine, etc.) have wide applications in defense, chemical industry, agriculture, and medicine. Current research indicates that hydrazine compounds can enter the human body through the respiratory tract, digestive tract, and skin absorption, causing central nervous system disorders, damage to the eyes and liver, and DNA damage. They possess clear carcinogenic and mutagenic properties and are a class of environmental pollutants that have attracted widespread attention. Therefore, hydrazine-containing wastewater requires treatment.

[0003] Studies have shown that although hydrazine is a relatively strong reducing agent, its oxidation to N2 at room temperature is extremely slow. A 20% reduction in concentration of hydrazine (5 mg / L at room temperature) in natural water with 8 mg / L dissolved oxygen takes 60 days, and conventional biological treatment methods are almost ineffective for treating hydrazine-containing wastewater. Therefore, it is necessary to explore other suitable methods for treating hydrazine-containing wastewater.

[0004] Chinese patent 202011056897.1 discloses a hydrazine-containing wastewater treatment process. After passing through a collection tank → evaporation system → catalytic reaction tank → multi-media filter → ultrafiltration system → reverse osmosis system → oxidation tank, the wastewater meets discharge standards or can be reused. However, this process is complex and requires significant equipment investment. Literature (HC Eun, JY Jung, SY Park, et al. Decomposition of a High-Concentration Hydrazine in Wastewater from A Chemical Decontamination Process of Anuclear Facility[J]. International Journal of Environmental Research, 2020, 14: 385-391) uses Cu(OH)2 as a catalyst and H2O2 as an oxidant. Under conditions of pH = 9.0 and n(H2O2) / n(N2H4) > 2.5, the hydrazine concentration in the effluent can reach below 10 ppb. However, this process has high requirements and is difficult to manage. Furthermore, existing methods do not address the generation of NH3 and secondary pollution of ammonia nitrogen during hydrazine decomposition.

[0005] In fact, hydrazine has the following two decomposition pathways:

[0006] N2H4→N2↑+2H2↑ (Decomposition path A)

[0007] 3N2H4→N2↑+4NH3 (Decomposition path B).

[0008] In actual operation, these two reactions are parallel reactions; at a certain temperature, the rates or product amounts of these two reactions satisfy a certain proportional relationship. We can define and calculate the degradation selectivity of hydrazine using the following formula:

[0009]

[0010]

[0011] In the formula, n dc (N2H4) and n pd (NH3) represents the amount of hydrazine decomposed and the amount of ammonia generated during the treatment process, respectively. According to the above definition, when the decomposition proceeds entirely along path A, n pd (NH3) = 0, S = 100%; when the decomposition proceeds entirely along path B, n pd (NH3) = (4 / 3) × n dc (N2H4), S=0.

[0012] In actual operation, changing the reaction temperature can change the product ratio. By using catalysts with different decomposition selectivity, the decomposition path of hydrazine can be controlled, and the reaction can even be made to proceed entirely along path A, so that the value of S tends to 100%.

[0013] On the other hand, hydrazine is a promising chemical hydrogen storage material, with anhydrous hydrazine containing up to 12.5% ​​hydrogen. For decades, researchers have been dedicated to the study of catalysts for highly selective hydrogen production (decomposition along pathway A) and have made a series of advances. The literature (SK Singh, XB Zhang, Q. Xu. Room-temperature Hydrogen Generation from Hydrous Hydrazine for Chemical Hydrogen Storage [J]. JACS, 2009, 131(29): 9894-9895) first reported a single-metal rhodium (Rh) nanocatalyst, which can ensure that the hydrazine decomposition reaction proceeds almost entirely along pathway A at room temperature. In order to overcome the disadvantage of high preparation cost of pure rhodium catalysts, researchers have tried a variety of bimetallic catalysts, among which nickel-based noble metal catalysts have the best comprehensive performance. These nickel-based noble metal catalysts include Ni-Pt system catalysts (SK Singh, Q. Xu. Bimetallic Ni-Pt Nanocatalysts for Selective Decomposition of Hydrazine in Aqueous Solution to Hydrogen at Room Temperature for Chemical Hydrogen Storage[J]. Inorganic Chemistry, 2010, 49, 6148–6152), Ni-Ir system catalysts (SK Singh, Q. Xu. Bimetallic Nickel-iridium nanocatalysts for hydrogen generation by decomposition of hydrous hydrazine[J]. Chemical Communications, 2010, 46(35): 6545-6547), and Ni-Pd system catalysts (D. Bhattacharjee, K. Mandal, S. Dasgupta. High Performance Nickel-palladium Nanocatalyst for Hydrogen Generation from Alkaline Hydrous Hydrazine at Room Temperature[J]. Journal of Power Sources, 2015, 287: 96-99, etc. Among them, the Ni-Pd system catalyst has a specific surface area of ​​150 m². 2 / g, composed of Ni60 Pd 40 The nanomaterial exhibits 100% selectivity for hydrazine decomposition under alkaline or neutral conditions, with a high decomposition rate. However, existing nickel-based noble metal catalysts still contain high levels of noble metals, leading to high catalyst costs. Furthermore, their complex preparation processes and poor product performance stability make them unsuitable for engineering preparation and application. Summary of the Invention

[0014] The purpose of this invention is to provide a catalyst suitable for the deep treatment of hydrazine-containing wastewater and its preparation method. This invention utilizes an existing nickel-phosphorus electroless plating solution system, under certain conditions, using SiO2 microspheres as a carrier and palladium (Pd) as a catalyst, to obtain a Ni-P-Pd@SiO2 nanocomposite catalyst. This product exhibits high activity and good decomposition selectivity, and is suitable for the deep degradation treatment of wastewater containing common hydrazine compounds (hydrazine hydrate, hydrazine sulfate, hydrazine nitrate, etc.).

[0015] The technical solution for achieving the objective of this invention is as follows:

[0016] A method for preparing a catalyst suitable for the advanced treatment of hydrazine-containing wastewater includes the following steps:

[0017] (1) Micro-etching of SiO2 microspheres: SiO2 microspheres are placed in an etching solution for etching treatment. After the treatment, they are centrifuged and washed. The etching solution is composed of the following components by weight percentage: 2-5% HF, 10-20% NH4F, and 75-88% H2O.

[0018] (2) Preparation of Ni-P-Pd@SiO2: The etched SiO2 microspheres were placed in a nickel-phosphorus reaction solution and stirred until they were evenly mixed. The temperature was raised to 80-95℃ and PdCl2 solution was added dropwise. After the reaction continued until no black particles were precipitated and no bubbles escaped, PdCl2 solution was slowly added dropwise to continue the aging reaction. After the reaction was completed, the mixture was centrifuged, washed with water, and dried to obtain the Ni-P-Pd@SiO2 catalyst. The composition of the nickel-phosphorus reaction solution was: 23 g / L nickel sulfate hexahydrate, 25 g / L sodium hypophosphite monohydrate, 25 g / L glycolic acid; or 23 g / L nickel sulfate hexahydrate, 20 g / L sodium hypophosphite monohydrate, 20 g / L lactic acid; or 23 g / L nickel sulfate hexahydrate, 15 g / L sodium hypophosphite monohydrate, 20 g / L sodium citrate, 5 g / L succinic acid.

[0019] In step (1), in order to improve the adhesion of active nanomaterials on SiO2 carrier, the SiO2 microspheres are first subjected to micro-etching treatment.

[0020] Further, in step (1), the average particle size of the SiO2 microspheres is 1 μm; the etching solution is composed of the following components by weight percentage: 3% HF, 15% NH4F, and 82% H2O.

[0021] Furthermore, in step (1), the etching temperature is 35±2℃ and the etching time is 5min.

[0022] In step (2), by changing the composition of the nickel-phosphorus reaction solution, the amount of palladium chloride added, and the reaction temperature, catalysts with different compositions can be obtained, whose stoichiometric formulas can be uniformly expressed as Ni α O β P γ Pd δ Si ε .

[0023] Furthermore, in step (2), the concentration of PdCl2 in the solution is c(PdCl2). 2+ =100mg / L.

[0024] Furthermore, in step (2), the aging reaction time is 1 hour.

[0025] The present invention provides a Ni-P-Pd@SiO2 catalyst prepared by the above preparation method.

[0026] Furthermore, this invention provides the application of the above-mentioned Ni-P-Pd@SiO2 catalyst in the advanced treatment of hydrazine-containing wastewater.

[0027] Specifically, the application method is as follows: the above-mentioned Ni-P-Pd@SiO2 catalyst is added to hydrazine-containing wastewater to catalyze the decomposition of hydrazine or its derivatives.

[0028] Furthermore, hydrazine derivatives include hydrazine hydrate, hydrazine sulfate, hydrazine nitrate, methylhydrazine, dimethylhydrazine, phenylhydrazine, etc.

[0029] Furthermore, the above application method is as follows: the above Ni-P-Pd@SiO2 catalyst and oxidant are added to hydrazine-containing wastewater to catalyze the decomposition of hydrazine or its derivatives.

[0030] Furthermore, the oxidizing agent is H2O2, calcium hypochlorite, etc.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) The Ni-P-Pd@SiO2 catalyst prepared by this invention has a low noble metal content, significantly reduces cost, and has a simple and mature preparation process, making it suitable for large-scale preparation.

[0033] (2) This invention utilizes SiO2 microspheres as a support, which reduces the aggregation of catalysts and improves the stability and catalytic effect of catalysts;

[0034] (3) The Ni-P-Pd@SiO2 catalyst prepared by this invention has high selectivity and good catalytic effect. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope image of the target product Ni-P-Pd@SiO2 from Example 1;

[0036] Figure 2 The surface composition analysis diagram (EDS layered image) of Ni-P-Pd@SiO2, the target product of Example 1;

[0037] Figure 3 The EDS energy spectrum of the target product Ni-P-Pd@SiO2 in Example 1 is shown below.

[0038] Figure 4 Example 2 illustrates the catalytic decomposition performance of several materials on hydrazine hydrate without an oxidant.

[0039] Figure 5 Example 2: Effect of temperature on hydrazine decomposition rate;

[0040] Figure 6 Example 3 shows the variation of hydrazine degradation efficiency under different catalysts with the amount of Ca(ClO)2 added;

[0041] Figure 7 Example 3: Changes in ammonia nitrogen in water treated with different catalysts as a function of Ca(ClO)2 dosage;

[0042] Figure 8 Example 4 illustrates the treatment effect of low-concentration hydrazine-containing wastewater.

[0043] Figure 9 The EDS spectrum of Cat-3 in Example 5;

[0044] Figure 10 This is a flow chart of the comprehensive treatment process for high-concentration hydrazine-containing wastewater in Example 5;

[0045] Figure 11 The following are the FT-IR spectra of the byproduct of Example 5 and hydrazine sulfate from the literature;

[0046] Figure 12 Example 5 illustrates the catalytic decomposition effect of the catalyst on actual wastewater. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0048] In the following examples, the methods for testing and calculating the percentage of hydrazine decomposition and the selectivity of hydrazine decomposition are as follows:

[0049] A certain amount of catalyst was added to hydrazine-containing wastewater, and after reacting for a certain time at a certain stirring speed, samples were taken to analyze the residual hydrazine concentration and the concentration of ammonia produced, according to formula...

[0050] E = [(C0 – C t ) / C0]×100%

[0051] Calculate the percentage of hydrazine decomposition.

[0052] According to the formula

[0053] S={n dc (N2H4)–(3 / 4)×n pd (NH3)] / n dc (N2H4)}×100%

[0054] Calculate the selectivity of hydrazine decomposition.

[0055] The analysis of hydrazine in high-concentration hydrazine solutions with a content greater than 1% (or 10000 mg / L) shall be carried out according to the method described in "4.3 Determination of hydrazine hydrate content" of HG / T 3259-2012 "Industrial Hydrazine Hydrate"; the analysis of hydrazine in low-concentration hydrazine solutions with a content less than 1% shall be carried out according to the method specified in HJ674-2013; the ammonia nitrogen concentration in the water sample shall be determined using a rapid ammonia nitrogen analyzer.

[0056] Example 1: Catalytic effect and degradation pathway selectivity of Ni-P-Pd@SiO2 on the oxidation of hydrazine hydrate by H2O2

[0057] 1. Preparation of Ni-P-Pd@SiO2 catalyst:

[0058] (1) Weigh 5g of commercially available SiO2 microspheres with an average particle size of 1μm, place them in 100mL of etching solution, etch for 5min under magnetic stirring at 200rpm, centrifuge, and wash three times with pure water before use. The etching solution consists of the following components by weight percentage: 3% HF, 15% NH4F, 82% H2O; the etching solution temperature is T = 35±2℃.

[0059] (2) Transfer 5g of etched SiO2 microspheres into a 250mL beaker containing 100mL of nickel-phosphorus reaction solution, turn on mechanical stirring, and after maintaining the temperature to 95℃, add c(Pd) dropwise. 2+ 0.5 mL of a PdCl2 solution with a concentration of 100 mg / L was added. After several hours, black particles precipitated and bubbles escaped. After the reaction was completed, 1.0 mL of the above palladium chloride solution was slowly added dropwise, and the reaction was continued for 1 hour. After centrifugation, the catalyst was washed three times with pure water and dried to obtain the Ni-P-Pd@SiO2 catalyst, denoted as Cat-1.

[0060] The nickel-phosphorus reaction solution consists of: 23 g / L nickel sulfate hexahydrate, 25 g / L sodium hypophosphite monohydrate, and 25 g / L glycolic acid.

[0061] Figure 1 The image shows a scanning electron microscope (SEM) image of Cat-1 particles. It can be seen that the Cat-1 particles are similar in size, with an average particle size of about 50 nm. Figure 2 and Figure 3 The images show the EDS layered image and EDS energy spectrum of Cat-1 particles, respectively. It can be seen that the surface components of Cat-1 particles are Ni, P, Pd, Si, and O. Based on their atomic percentages, their stoichiometric formula can be expressed as Ni... 0.54 O 0.19 P 0.17 Pd 0.002 Si 0.087 .

[0062] 2. Cat-1 catalyzes the oxidation of hydrazine hydrate by H2O2

[0063] (1) Take 100 mL of 40% hydrazine hydrate solution (AR), dilute it with pure water to 1000 mL, and record it as "hydrazine hydrate water sample" for later use. According to the method described in HG / T 3259-2012, the hydrazine hydrate content in the above "hydrazine hydrate water sample" is determined to be 3.85% or the hydrazine content is 2.46%, that is, the hydrazine content in each liter of water sample is 24.6 g.

[0064] (2) Take 100 mL of the above hydrazine hydrate water sample into seven 250 mL Erlenmeyer flasks (A, B1, B2, C1, C2, D1, and D2). Add H2O2 and Cat-1 according to Table 1. Keep the temperature constant at 25℃ for 30 min in a shaker. Then add 30% analytical grade H2O2 dropwise at a rate of 1 mL / min according to Table 1. After the addition is completed, keep the temperature constant for another 30 min. Then take samples to analyze the hydrazine content and ammonia nitrogen content. Calculate the mass of the substances based on the final volume of the water sample. The results are shown in Table 1.

[0065] Table 1. Treatment effect of hydrazine hydrate on water samples

[0066]

[0067]

[0068] The amount of hydrogen peroxide added is determined according to the reaction formula (N2H4+2H2O2= N2↑+4H2O) with an excess of 10%.

[0069] The experiments in groups A and C in Table 1 show that the catalyst Cat-1 can promote the decomposition of hydrazine at room temperature; the experiments in groups B, C, and D show that the catalyst of the present invention has excellent selectivity for the degradation pathway of hydrated hydrazine.

[0070] Example 2: Comparison of the catalytic decomposition performance of several catalytic materials for hydrazine hydrate in the absence of oxidant.

[0071] (1) Take five 1000 mL beakers (A, B, C, D, and E), add 1000 mL of hydrazine hydrate solution with a concentration of 2500 mg / L to each beaker, and add MnO2 (MW Rophael. Kinetics of Reduction of Manganese Dioxides by Hydrazine and of the Catalytic Decomposition of Hydrogen Peroxide. Surface Technology, 1982, 16(3): 235-242), Cu(OH)2 (HC Eun, J-YJung, SY Park, et al. Decomposition of a High-Concentration Hydrazine in Wastewater from AChemical Decontamination Process of ANuclear Facility [J]. International Journal of Environmental Research, 2020, 14: 385–391) and Cat-1 to beakers B, C, and D respectively. 0.5g of a platinum-plated titanium mesh (denoted as Pt@Ti, a commonly used electroplating anode material) was added to beaker E. The surface air was replaced with nitrogen, and the beaker was sealed with a plastic film and magnetically stirred at 120 rpm at room temperature. The supernatant was taken at regular intervals, and the hydrazine concentration in the water sample was measured to calculate the hydrazine decomposition percentage E. Without the addition of an oxidant, the catalytic decomposition performance of several materials on hydrated hydrazine was as follows: Figure 4 As shown.

[0072] (2) Take five 250 mL Erlenmeyer flasks and add 100 mL of hydrazine-containing water sample with an initial concentration of 2500 mg / L to each. After sealing the flasks, place them in a water bath with magnetic stirring. Maintain the temperature at 20℃, 30℃, 40℃, 50℃, and 60℃ respectively, then add 0.05 g of Cat-1. Continue stirring and reacting at the same temperature for 60 min, then transfer to an ice-water bath at 0℃ to terminate the reaction. Take samples to analyze the residual hydrazine concentration in each water sample. Perform a blank test without catalyst using the same method. The change in the hydrazine decomposition rate with temperature is shown below. Figure 5 As shown.

[0073] Figure 4The results show that, in the absence of oxidants, MnO2, Cu(OH)2 and Pt@Ti have a slight catalytic effect on the decomposition of low-concentration hydrazine hydrate, but it is far less significant than that of Cat-1. After Cat-1 has been used for 8 hours at room temperature, the decomposition rate of hydrazine hydrate reaches more than 98%.

[0074] Figure 5 The results indicate that temperature has a significant impact on the decomposition of hydrazine. However, in the absence of a catalyst, the decomposition rate of hydrazine is slow, making it almost useless for treating hydrazine-containing wastewater. But in the presence of catalyst Cat-1, the decomposition rate of hydrazine increases rapidly with increasing temperature, initially increasing exponentially, and then leveling off.

[0075] Example 3: Catalytic effect and degradation pathway selectivity of Ni-P-Pd@SiO2 on the oxidation of hydrazine sulfate by calcium hypochlorite

[0076] 1. Preparation of Ni-P-Pd@SiO2 catalyst:

[0077] (1) Same as Example 1.

[0078] (2) Transfer 5g of etched SiO2 microspheres into a 250mL beaker containing 100mL of nickel-phosphorus reaction solution, turn on mechanical stirring, and after maintaining the temperature to 90℃, add c(Pd) dropwise. 2+ Add 0.5 mL of a PdCl2 solution with a concentration of 100 mg / L. After several hours, black particles precipitate and bubbles escape. After the reaction is complete, slowly add another 0.5 mL of the above PdCl2 solution, continue the aging reaction for 1 hour, centrifuge, wash three times with pure water, and dry for later use to obtain the Ni-P-Pd@SiO2 catalyst, denoted as Cat-2.

[0079] The nickel-phosphorus reaction solution consists of: 23 g / L nickel sulfate hexahydrate, 20 g / L sodium hypophosphite monohydrate, and 20 g / L DL-lactic acid.

[0080] 2. Cat-2 catalyzed oxidation of hydrazine sulfate by calcium hypochlorite

[0081] (1) Weigh 10g of analytical grade hydrazine sulfate and dissolve it in 4L of pure water. Record it as "hydrazine sulfate water sample". The concentration of hydrazine in the water sample was measured to be 606mg / L according to the method of standard HJ 674-2013.

[0082] (2) Take three 1000mL beakers (A, B, and C), add 1000mL of the above hydrazine sulfate water sample to each, and add 500mg of Cu(OH)2 and Cat-2 to beakers B and C respectively. Stir at 120rpm at room temperature. Add 500mg of powdered calcium hypochlorite (Ca(ClO)2, AR) to the beakers every 10min. Before the next addition of calcium hypochlorite, take a sample and analyze the concentrations of hydrazine and ammonia nitrogen in the water sample. The relationship between the changes of hydrazine and ammonia nitrogen with the amount of calcium hypochlorite added is summarized as follows: Figure 6 , Figure 7 .

[0083] Figure 6 , Figure 7 The results showed that, under the condition of using calcium hypochlorite as an oxidant, the catalyst Cat-2 can effectively improve the degradation efficiency and degradation rate of hydrazine sulfate, and exhibit excellent degradation selectivity.

[0084] Example 4: Catalytic decomposition effect of Cat-2 on low-concentration hydrazine-containing wastewater

[0085] Take four 1000mL beakers (A, B, C, and D), and add 1000mL of a hydrazine-containing water sample (CO(N₂H₄) = 20mg / L) to each. Stir at 120rpm at room temperature. Add 0.5g of Cat⁻², 1g of Ca(ClO)₂, and 0.5g of Cat⁻² + 1g of Ca(ClO)₂ to beakers B, C, and D, respectively. Take samples at regular intervals and analyze the concentration of hydrazine in the water samples. The change in the concentration of hydrazine in each water sample over time is shown in the figure below. Figure 8 .

[0086] Figure 8 The results showed that the concentration of hydrazine changed very little under conditions without the addition of catalyst and oxidant; under the condition of only adding Cat-2, the concentration of hydrazine decreased linearly with time, and could be degraded to below 0.1 mg / L after a sufficiently long time; under the condition of only adding calcium hypochlorite as oxidant, although the initial addition of calcium hypochlorite was greatly excessive [n0(ClO) / n0(N2H4)≈20], it was still not possible to degrade hydrazine to a level below 0.1 mg / L; when Cat-2 was used in combination with calcium hypochlorite, the degradation rate could be greatly improved, and hydrazine could be degraded to a level below 0.1 mg / L after about 3 hours at room temperature.

[0087] Example 5: Treatment effect of Cat-3 on a specific hydrazine-containing wastewater

[0088] 1. Preparation of Ni-P-Pd@SiO2 catalyst:

[0089] (1) Same as Example 1.

[0090] (2) Transfer 5g of etched SiO2 microspheres into a 250mL beaker containing 100mL of nickel-phosphorus reaction solution, turn on mechanical stirring, and after maintaining the temperature at 80℃, add c(Pd) dropwise. 2+ Adding 0.5 mL of a 100 mg / L PdCl2 solution resulted in the precipitation of black particles and the escape of bubbles after several hours. After the reaction was complete, 0.3 mL of the above palladium chloride solution was slowly added dropwise, and the reaction was allowed to continue for 1 hour. The mixture was then centrifuged, washed three times with pure water, and dried for later use to obtain the Ni-P-Pd@SiO2 catalyst, designated Cat-3. EDS analysis of Cat-3 is shown below. Figure 9 As shown.

[0091] The nickel-phosphorus reaction solution consists of: 23 g / L nickel sulfate hexahydrate, 15 g / L sodium hypophosphite monohydrate, 20 g / L sodium citrate, and 5 g / L succinic acid.

[0092] 2. Treatment of a specific hydrazine-containing wastewater using Cat-3

[0093] A certain engineering-grade wastewater containing hydrazine contains hydrazine hydrate, hydrazine nitrate, and other hydrazine compounds, as well as certain concentrations of nitroglycerin (NG), N,N′-dimethyl-N,N′-diphenylurea (C2), and triethylene glycol nitrate (TEGN), etc. Its comprehensive water quality indicators are shown in Table 2.

[0094] Table 2 Water quality indicators of a certain hydrazine-containing wastewater

[0095]

[0096] Due to the high hydrazine content in the actual wastewater, and considering factors such as resource conservation, cost reduction, and environmental protection, the wastewater treatment is divided into two steps: the first step is hydrazine recovery, and the second step is hydrazine degradation. The comprehensive treatment process flow is as follows: Figure 10 As shown, the details are as follows:

[0097] (1) Hydrazine recovery reaction. Take 500 mL of the wastewater shown in Table 2 and add it to a 1000 mL three-necked flask equipped with a stirrer and placed in a cold bath. Set the cold bath temperature to -5℃ to 0℃. When the temperature drops to near 0℃, slowly add 55 mL of analytical grade concentrated sulfuric acid, keeping the solution temperature no higher than 5℃ during the addition. After the addition is complete, keep the reaction at this temperature for 60 min, then add 20 mL of anhydrous methanol and continue stirring slowly for another 60 min. Filter while cold and wash the solid with a small amount of ice water to obtain 118.8 g of a pale yellow solid and approximately 497 mL of tailings water. Take a small amount of the solid for infrared detection; its FT-IR spectrum is shown below. Figure 11 Comparison with the infrared spectrum of hydrazine sulfate indicates that the solid is the byproduct hydrazine sulfate (N2H4·H2SO4).

[0098] (2) Advanced treatment of hydrazine-containing tailwater. Analysis showed the residual hydrazine concentration in the tailwater was 3500 mg / L. Four 250 mL Erlenmeyer flasks (A, B, C, and D) were used, and 100 mL of the aforementioned tailwater was added to each. The mixture was magnetically stirred at R = 120 rpm and kept at a constant temperature of 35°C. Then, 50 mg (0.5 g / L) each of Cat-1, Cat-2, and Cat-3 were added to flasks B, C, and D respectively. Samples were taken every 2 hours to determine the hydrazine concentration. The decomposition effects of each catalyst on hydrazine are as follows: Figure 12 As shown.

[0099] Figure 12 This indicates that although the composition of the catalyst in this invention has some influence on the catalytic effect, the catalytic effect is very significant. This embodiment also shows that other high-concentration pollutants present in the wastewater (such as NG, C2, CH3OH, TEGN, etc.) have little effect on the effect of the Ni-P-Pd@SiO2 catalyst.

Claims

1. The application of Ni-P-Pd@SiO2 catalyst in the advanced treatment of hydrazine-containing wastewater, characterized in that, Ni-P-Pd@SiO2 catalyst and oxidant are added to hydrazine-containing wastewater to catalyze the decomposition of hydrazine or its derivatives. The oxidant is H2O2 or calcium hypochlorite. The Ni-P-Pd@SiO2 catalyst was prepared by the following steps: (1) Micro-etching of SiO2 microspheres: SiO2 microspheres are placed in an etching solution for etching treatment. After the treatment is completed, they are separated by centrifugation and washed. The etching solution is composed of the following components by weight percentage: 2-5% HF, 10-20% NH4F, and 75-88% H2O. (2) Preparation of Ni-P-Pd@SiO2: The etched SiO2 microspheres were placed in the nickel-phosphorus reaction solution, stirred and mixed evenly, and then heated to 80-95℃. PdCl2 solution was added dropwise. After the reaction continued until no black particles were precipitated and no bubbles escaped, PdCl2 solution was slowly added dropwise to continue the aging reaction. After the reaction was completed, the mixture was centrifuged, washed with water, and dried to obtain the Ni-P-Pd@SiO2 catalyst. The composition of the nickel-phosphorus reaction solution was: 23 g / L nickel sulfate hexahydrate, 25 g / L sodium hypophosphite monohydrate, 25 g / L glycolic acid; or 23 g / L nickel sulfate hexahydrate, 20 g / L sodium hypophosphite monohydrate, 20 g / L DL-lactic acid; or 23 g / L nickel sulfate hexahydrate, 15 g / L sodium hypophosphite monohydrate, 20 g / L sodium citrate, 5 g / L succinic acid.

2. The application according to claim 1, characterized in that, In step (1), the average particle size of the SiO2 microspheres is 1 mm; the etching solution is composed of the following components by weight percentage: 3% HF, 15% NH4F, 82% H2O; the etching temperature is 35±2℃ and the etching time is 5 min.

3. The application according to claim 1, characterized in that, In step (2), in the PdCl2 solution c (Pd 2+ = 100mg / L.

4. The application according to claim 1, characterized in that, In step (2), the aging reaction time is 1 h.

5. The application according to claim 1, characterized in that, The hydrazine derivatives are hydrazine hydrate, hydrazine sulfate, hydrazine nitrate, methylhydrazine, dimethylhydrazine, or phenylhydrazine.

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