Method for detecting total nitrogen content in coking wastewater

Abstract

The application provides a detection method for total nitrogen content in coking wastewater, and belongs to the technical field of detection. The detection method is characterized by the following steps: preparing total nitrogen standard solutions with different concentrations by using potassium nitrate, and then digesting by using nano-Fe3O4 and hydrogen peroxide; then nitrifying by using disodium metavanadate and sulfur-phosphorus mixed acid; then determining the absorbance by using visible spectrophotometry, and then drawing a standard curve of total nitrogen; taking coking wastewater, digesting by using nano-Fe3O4 and hydrogen peroxide, and then nitrifying by using disodium metavanadate and sulfur-phosphorus mixed acid; then determining the absorbance by using visible spectrophotometry, and then substituting into the standard curve of total nitrogen, and then calculating the total nitrogen content in the coking wastewater. The method can be used for detecting the total nitrogen content in complex water quality such as coking wastewater, and has the advantages of simple operation, convenience, high accuracy, economy and practicality.

Description

Technical Field

[0001] This invention relates to a method for detecting total nitrogen content, and more particularly to a method for detecting total nitrogen content in coking wastewater. Background Technology

[0002] Total nitrogen (TNI) refers to the nitrogen content in soluble and suspended particles, including the sum of nitrogen from nitrite, nitrate, inorganic ammonium salts, dissolved ammonia, and most organic nitrogen-containing compounds in water. Coking wastewater contains a significant amount of nitrogenous compounds that are difficult to remove. Coking wastewater is mainly generated during coal coking, coal gas purification, and the production and refining of chemical products, and is a typical type of recalcitrant industrial wastewater. High concentrations and diverse types of nitrogenous pollutants are key characteristics of this type of wastewater, which determines the complexity of its treatment process. Under the current wave of coking capacity replacement and the industry's demand for zero emissions, the detection of TNI content in coking wastewater has become an essential step to ensure compliance with TNI standards. Currently, the alkaline potassium persulfate digestion ultraviolet spectrophotometric method is generally used for TNI detection in wastewater. However, in actual testing of coking wastewater, the results have been found to be less than ideal. This may be because this method cannot completely eliminate nitrogenous compounds during the digestion of coking wastewater with its more complex composition, and the oxidant may not decompose completely. Summary of the Invention

[0003] To address the above problems, this invention provides a method for detecting the total nitrogen content in coking wastewater.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for detecting total nitrogen content in coking wastewater, the method comprising the following steps:

[0006] 1) Prepare total nitrogen standard solutions of different concentrations using potassium nitrate;

[0007] 2) Take total nitrogen standard solutions of different concentrations, add deionized water, then add nano-ferric oxide and hydrogen peroxide, microwave digest, cool, separate the nano-ferric oxide, filter again, add disodium chromolate and sulfuric acid mixed with phosphoric acid to the filtrate to carry out nitration reaction, produce yellow nitrated products, and then use visible spectrophotometry to measure the absorbance of the nitrated products corresponding to different concentrations of total nitrogen standard solutions at 410 nm. Based on the total nitrogen concentration in the total nitrogen standard solutions of different concentrations and the absorbance of the corresponding nitrated products, plot the total nitrogen standard curve;

[0008] 3) Take coking wastewater, add deionized water, then add nano-ferric oxide and hydrogen peroxide, microwave digest, cool, separate the nano-ferric oxide, filter again, add disodium chromolate and sulfuric acid mixed with sulfuric acid and phosphoric acid to the filtrate in sequence to carry out nitration reaction, produce yellow nitrated products, then use visible spectrophotometry to measure the absorbance of the nitrated products prepared from coking wastewater at 410 nm, substitute the absorbance of the nitrated products corresponding to the obtained coking wastewater into the standard curve of total nitrogen, and calculate the total nitrogen content in the coking wastewater.

[0009] Furthermore, in step 2), the volume-to-weight ratio of total nitrogen standard solutions of different concentrations to nano-ferric oxide is 1 mL: 0.003–0.005 g.

[0010] In step 3), the volume-to-weight ratio of coking wastewater to nano-ferric oxide is 1 mL: 0.003–0.005 g.

[0011] Furthermore, in step 2), the concentration of hydrogen peroxide is 30 wt%, and the volume ratio of total nitrogen standard solutions of different concentrations to hydrogen peroxide is 1:0.4 to 0.5.

[0012] In step 3), the concentration of hydrogen peroxide is 30 wt%, and the volume ratio of coking wastewater to hydrogen peroxide is 1:0.4 to 0.5.

[0013] Furthermore, in step 2), the microwave digestion temperature is 80–90°C, the power is 1100–1200W, and the time is 8–10 min;

[0014] In step 3), the microwave digestion temperature is 80-90℃, the power is 1100-1200W, and the time is 8-10min.

[0015] Furthermore, in step 2), the volume-to-weight ratio of the filtrate prepared from the total nitrogen standard solution of different concentrations to disodium chromotropic acid is 1 mL: 0.01–0.012 g.

[0016] In step 3), the volume-to-weight ratio of the filtrate prepared from the coking wastewater to disodium chromotropic acid is 1 mL: 0.01–0.012 g.

[0017] Furthermore, in step 2), the standard curve for total nitrogen is y = 56.334x - 0.0019, R0 2 =0.9996.

[0018] Furthermore, in step 2), the volume ratio of total nitrogen standard solutions of different concentrations to deionized water is 1:3;

[0019] In step 3), the volume ratio of coking wastewater to deionized water is 1:3.

[0020] Furthermore, in steps 2) and 3), the sulfuric-phosphoric acid mixture is made by mixing sulfuric acid with a concentration of 98% and concentrated phosphoric acid with a concentration of ≥85% in a volume ratio of 6:4.

[0021] Furthermore, in steps 2) and 3), nano-ferric oxide is prepared by adding ferric sulfate and ferric chloride to water and then using ammonia as a co-precipitant.

[0022] Furthermore, in steps 2) and 3), the nitration reaction occurs in a strongly acidic environment (i.e., under the action of a sulfuric-phosphoric acid mixture), utilizing the nitrate ions (nitrate ions obtained after digestion) contained in the filtrate to react with chromotropic acid. The chemical reaction formula for the nitration reaction is as follows:

[0023]

[0024] The beneficial effects of the method for detecting total nitrogen content in coking wastewater of the present invention are as follows:

[0025] This invention uses a specific amount of hydrogen peroxide combined with nano-ferric oxide to effectively and completely decompose nitrogenous substances in complex coking wastewater without being affected by other components. Furthermore, by converting the nitrate ions obtained after decomposition into yellow nitration products and then measuring the content of the yellow nitration products, it is possible to avoid the influence of absorbance caused by incompletely decomposed hydrogen peroxide during the detection process, which would affect the measurement results.

[0026] This invention selects specific process parameters and uses a specific amount of hydrogen peroxide to microwave digest nitrogen-containing substances in coking wastewater under the catalysis of nano-ferric oxide. This not only reduces the digestion temperature but also shortens the digestion time. The entire process is simple to operate and ensures that all nitrogen-containing compounds are digested, guaranteeing the accuracy of the measurement results. At the same time, this invention converts the nitrate ions obtained from complete digestion into yellow nitration products for absorbance measurement, avoiding the influence of incomplete hydrogen peroxide decomposition on the absorbance of the results (this is because hydrogen peroxide does not produce absorbance during visible spectrophotometry at 410 nm, so undecomposed hydrogen peroxide will not affect the results).

[0027] The method of this invention can be used to detect the total nitrogen content in complex water quality such as coking wastewater. The whole method is simple to operate, convenient and fast, highly accurate, economical and practical. Attached Figure Description

[0028] Figure 1 This is the standard curve of total nitrogen at a wavelength of 410 nm in Example 1 of the present invention;

[0029] Figure 2 This is the standard curve of alkaline potassium persulfate-total nitrogen at a wavelength of 410 nm in Comparative Example 10 of this invention;

[0030] Figure 3 This is the calibration curve of total nitrogen in Comparative Example 11 of this invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] Example 1: A method for detecting total nitrogen content in coking wastewater

[0033] This embodiment describes a method for detecting the total nitrogen content in coking wastewater, specifically including the following steps:

[0034] 1) Take 60 mL of 98% concentrated sulfuric acid and slowly add it to 40 mL of 85% or higher concentrated phosphoric acid (the concentration of concentrated phosphoric acid in this example is 85%). Stir slowly with a glass rod while adding the solution until it is mixed evenly. Cool to room temperature and let stand for 72 hours to obtain sulfuric-phosphoric acid mixture for later use.

[0035] Dissolve 1.0g of disodium chromotropic acid in 50mL of water. After it is completely dissolved, make up the volume to 100mL to obtain a disodium chromotropic acid solution for later use (the disodium chromotropic acid solution should be prepared fresh before use).

[0036] Take FeSO4·7H2O and FeCl3·6H2O with a molar ratio of 1:2 to 2.1 (in this example, the molar ratio of FeSO4·7H2O and FeCl3·6H2O is 1:2), add deionized water, stir to dissolve, slowly add a slightly excess of NH3·H2O as a co-precipitant, black particles appear, let stand for 1 to 2 hours (1.5 hours in this example), then separate them using a very strong magnet, wash with water, and then dry in a vacuum drying oven at 50°C for 12 hours to obtain nano-sized iron(III) oxide, for later use;

[0037] After potassium nitrate was dried at 105-110℃ for 2 hours (the drying temperature in this example was 110℃), an appropriate amount was taken and dissolved in deionized water to prepare a series of total nitrogen standard solutions with different concentrations of 0 mg / L, 2 mg / L, 5 mg / L, 8 mg / L, 10 mg / L, 12.5 mg / L, 16 mg / L and 20 mg / L.

[0038] 2) Take 1.00 mL of the total nitrogen standard solutions of different concentrations mentioned above, add 3.0 mL of deionized water, place them in a 10 mL digestion tube, then add 0.005 g of nano-ferric oxide and 0.4 mL of 30 wt% hydrogen peroxide. Seal the tube and place it in a microwave digestion furnace. Digest at 90°C and 1200 W for 10 min. Cool to room temperature, and use a strong magnet to recover and separate the nano-ferric oxide (the recovered nano-ferric oxide can be reused). Filter. Add 1 mL of disodium chromotropic acid solution (equivalent to 0.01 g of disodium chromotropic acid) to the obtained filtrate, tighten the cap, shake vigorously up and down for 30 seconds, let stand for 3 minutes, then transfer 2 mL of the obtained reaction solution to a colorimetric tube, slowly add 8 mL of sulfuric-phosphoric acid mixture (generally, the addition time is 2 minutes), tighten the cap, invert the tube 10 times, cool with water for 10 minutes, and then let stand at room temperature for 10 minutes. Under a strongly acidic environment (with the action of sulfuric-phosphoric acid mixture), the nitrate ions in the system undergo a nitration reaction with the chromotropic acid to produce a yellow nitrated product. The chemical reaction formula for the nitration reaction between nitrate ions and chromotropic acid is as follows:

[0039]

[0040] Using water as a reference, the absorbance was measured at 410 nm using a visible spectrophotometer. The absorbance of the nitration products prepared corresponding to different concentrations of total nitrogen standard solutions was measured at 410 nm using visible spectrophotometry. Since the absorbance of the nitration products is linearly related to the content of the nitration products (positively correlated), and the content of the nitration products is also linearly related to the total nitrogen concentration in the corresponding total nitrogen standard solution (positively correlated), a standard curve of total nitrogen was plotted based on the total nitrogen concentration in the total nitrogen standard solutions of different concentrations and the absorbance of the corresponding nitration products.

[0041] The total nitrogen concentration in the total nitrogen standard solutions of different concentrations and the absorbance of the corresponding nitration products are shown in Table 1.

[0042] Table 1. Summary of Total Nitrogen Concentration and Corresponding Absorbance.

[0043]

[0044] A calibration curve was plotted with the total nitrogen (as N) concentration (mg / L) in standard solutions of different concentrations as the ordinate (x) and the absorbance values ​​of the corresponding nitration products as the abscissa (x). See [reference needed]. Figure 1 The standard curve for total nitrogen was obtained as y = 56.334x - 0.0019, R0. 2 =0.9996.

[0045] 3) Take 1.00 mL of coking wastewater, add 3.0 mL of deionized water, place it in a 10 mL digestion tube, then add 0.005 g of nano-ferric oxide and 0.4 mL of 30 wt% hydrogen peroxide. After sealing, place it in a microwave digestion furnace and digest at 90 °C and 1200 W for 10 min. After cooling to room temperature, use a strong magnet to recover and separate the nano-ferric oxide. Filter, add 1 mL of disodium chromotropic acid solution (equivalent to 0.01 g of disodium chromotropic acid) to the filtrate, tighten the lid and shake vigorously up and down for 30 s. After standing for 3 min, transfer 2 mL of the resulting reaction solution to a colorimetric tube, slowly add 8 mL of sulfuric-phosphoric acid mixture, tighten the lid and invert 10 times, cool with water for 10 min, and then stand at room temperature for 10 min. Under a strongly acidic environment, nitrate ions and chromotropic acid undergo a nitration reaction to produce a yellow nitrated product. The chemical reaction formula for the nitration reaction between nitrate and chromotropic acid is as follows:

[0046]

[0047] Using water as a reference, the absorbance of the nitration products prepared from coking wastewater was measured at 410 nm using a visible spectrophotometer. The absorbance was then substituted into the standard curve of total nitrogen to calculate the total nitrogen content in the coking wastewater.

[0048] When the total nitrogen content in the coking wastewater is <1 mg / L, retain two decimal places; when the total nitrogen content in the coking wastewater is ≥1 mg / L, retain three significant figures.

[0049] In this embodiment, the total nitrogen content (calculated as N) in the coking wastewater was measured to be 242.256 mg / L.

[0050] Furthermore, in practical applications, if the standard curve for total nitrogen is known, the absorbance obtained after treating the coking wastewater using step 3) can be directly substituted into the known standard curve for total nitrogen calculation. There is no need to repeat steps 1) and 2) to plot the standard curve for total nitrogen.

[0051] Phenol, xylenol, and benzo[a]pyrene in a weight ratio of 1:1:1:1 were used as COD substances, along with quinoline, benzonitrile, aniline, indole, pyridine, and NH4 in a weight ratio of 1:1:1:1:1:1:1:1. +-N, sodium thiocyanate, and sodium cyanide are used together as total nitrogen substances; appropriate amounts of the above-mentioned COD substances, the above-mentioned total nitrogen substances, zinc, chromium, and lead are weighed, added to deionized water, and ultrasonically dispersed and dissolved to prepare a simulated coking wastewater, wherein the COD content of the simulated coking wastewater is 5500 mg / L (theoretical value calculated based on the amount of COD substances added), the total nitrogen content (calculated as N) is 245.001 mg / L (theoretical value calculated based on the amount of total nitrogen substances added), the zinc content is 4.50 mg / L, the chromium content is 1.80 mg / L, and the lead content is 1.50 mg / L.

[0052] Using the method in step 3), the above-mentioned imitation coking wastewater was treated, and the absorbance of the nitration product prepared corresponding to the imitation coking wastewater was measured. The absorbance was then substituted into the standard curve of total nitrogen drawn in step 2) for calculation. The total nitrogen content in the imitation coking wastewater was measured to be 244.984 mg / L.

[0053] Examples 2-5: Methods for determining total nitrogen content in coking wastewater

[0054] Examples 2-5 are methods for detecting total nitrogen content in coking wastewater. Their steps are basically the same as in Example 1, differing only in the process parameters, as detailed in Table 1.

[0055] Table 1. Summary of process parameters in Examples 2-5

[0056]

[0057]

[0058] The process steps and parameters for other parts of Examples 2 to 5 are the same as those in Example 1, and the effects are also basically the same as those in Example 1, so they will not be repeated here.

[0059] Experimental Example 1: Comparative Experiment

[0060] Comparative Examples 1-7 are comparative experiments of step 3) of the method for detecting total nitrogen content in coking wastewater in Example 1. The simulated coking wastewater prepared in Example 1 was used as the analyte for total nitrogen content determination, and the calculation was performed using the standard curve for total nitrogen plotted in step 2) of Example 1. The process used in step 3) was also basically the same, with the only difference being:

[0061] In step 3) of Comparative Example 1, only the amount of nano-ferric oxide was adjusted to 0.001 g, while other amounts and parameters remained unchanged. The absorbance of the nitration product corresponding to the simulated coking wastewater prepared in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 222.634 mg / L. It can be seen that reducing the amount of nano-ferric oxide leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because reducing the amount of nano-ferric oxide may prevent the complete decomposition of nitrogenous substances in the simulated coking wastewater, resulting in a lower measurement result.

[0062] In step 3) of Comparative Example 2, only the amount of 30wt% hydrogen peroxide was adjusted to 0.2 mL, while other amounts and parameters remained unchanged. The absorbance of the nitration product corresponding to the simulated coking wastewater prepared in Example 1 was measured, and then the total nitrogen content was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1. The measured total nitrogen content in the simulated coking wastewater was 205.895 mg / L. It can be seen that reducing the amount of hydrogen peroxide leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because reducing the amount of hydrogen peroxide may prevent the complete decomposition of nitrogenous substances in the simulated coking wastewater, resulting in a lower measurement result.

[0063] In step 3) of Comparative Example 3, only the microwave digestion temperature was adjusted to 60℃, while other dosages and parameters remained unchanged. The absorbance of the nitration product prepared from the simulated coking wastewater in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 211.781 mg / L. It can be seen that lowering the microwave digestion temperature leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because lowering the microwave digestion temperature may prevent the complete digestion of nitrogenous substances in the simulated coking wastewater, resulting in a lower measurement result.

[0064] In step 3) of Comparative Example 4, only the microwave digestion temperature was adjusted to 125℃, while other dosages and parameters remained unchanged. The absorbance of the nitration product prepared corresponding to the simulated coking wastewater prepared in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 237.659 mg / L. It can be seen that increasing the microwave digestion temperature leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because increasing the microwave digestion temperature causes partial hydrolysis of hydrogen peroxide, resulting in incomplete digestion of nitrogenous substances in the simulated coking wastewater, thus lowering the measured result.

[0065] In step 3) of Comparative Example 5, only the microwave digestion power was adjusted to 800W, while other dosages and parameters remained unchanged. The absorbance of the nitration product prepared from the simulated coking wastewater in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 228.647 mg / L. It can be seen that reducing the microwave digestion power leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because reducing the microwave digestion power results in incomplete digestion of nitrogenous substances in the simulated coking wastewater, leading to a decrease in the measured result.

[0066] In step 3) of Comparative Example 6, only the microwave digestion power was adjusted to 1500W, while other dosages and parameters remained unchanged. The absorbance of the nitration product corresponding to the simulated coking wastewater prepared in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 236.589 mg / L. It can be seen that increasing the microwave digestion power leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because increasing the microwave digestion power leads to partial hydrolysis of hydrogen peroxide, resulting in incomplete digestion of nitrogenous substances in the simulated coking wastewater, thus reducing the measured result.

[0067] In step 3) of Comparative Example 7, only the microwave digestion time was adjusted to 5 minutes, while other dosages and parameters remained unchanged. The absorbance of the nitration product prepared from the simulated coking wastewater in Example 1 was measured. Then, the total nitrogen content in the simulated coking wastewater was calculated using the standard curve of total nitrogen drawn in step 2) of Example 1, and the measured total nitrogen content was 217.893 mg / L. It can be seen that reducing the microwave digestion time leads to a decrease in the measured total nitrogen content in the simulated coking wastewater. This may be because reducing the microwave digestion time may result in incomplete digestion of nitrogenous substances in the simulated coking wastewater, leading to a decrease in the measured result.

[0068] The method for determining the total nitrogen content in the simulated coking wastewater prepared in Example 1 in Comparative Example 8 includes the following steps:

[0069] Dissolve 4.0 g of potassium persulfate (nitrogen content less than 0.0005%) in 60 mL of water (it can be heated in a 50 °C water bath until completely dissolved) to obtain a potassium persulfate solution;

[0070] Dissolve 1.5g of sodium hydroxide (containing less than 0.0005% nitrogen) in 30mL of water. After the sodium hydroxide solution cools to room temperature, a sodium hydroxide solution is obtained.

[0071] Mix potassium persulfate solution and sodium hydroxide solution, and then dilute to 100 mL to obtain an alkaline potassium persulfate solution.

[0072] Take 1.00 mL of the simulated coking wastewater prepared in Example 1, add 3.0 mL of deionized water, place it in a 10 mL digestion tube, then add 3.0 mL of alkaline potassium persulfate solution, seal the tube, and place it in a microwave digestion furnace. Digest at 125°C and 1200 W for 30 min. Cool to room temperature, add 1 mL of disodium chromotropic acid solution (equivalent to 0.01 g disodium chromotropic acid) to the resulting digestion solution, tighten the lid, shake vigorously up and down for 30 s, let stand for 3 min, transfer 2 mL of the resulting reaction solution to a colorimetric tube, and slowly add dropwise. 8 mL of sulfur-phosphoric acid mixture was tightly capped and inverted 10 times. After water cooling for 10 minutes, it was left to stand at room temperature for 10 minutes. Under a strongly acidic environment, nitrate ions reacted with chromotropic acid to produce a yellow nitrated product. (Since the nitrated product produced in Comparative Example 8 and Example 1 is the same, and the subsequent visible spectrophotometric determination method is also the same, to reduce the difference from Example 1, the standard curve of total nitrogen drawn in step 2 of Example 1 is directly used for calculation, instead of using alkaline potassium persulfate as a digestion reagent to redraw the standard curve). Using water as a reference, the absorbance of the nitrated product prepared from the imitation coking wastewater was measured at 410 nm using a visible spectrophotometer. Substituting this into the standard curve of total nitrogen drawn in step 2 of Example 1, the total nitrogen content in the imitation coking wastewater was calculated to be 244.178 mg / L.

[0073] In Comparative Example 9, the total nitrogen content in the simulated coking wastewater was determined using the method in Comparative Example 8, with the only difference being that the microwave digestion temperature was 90℃, the power was 1200W, and the time was 10min. The total nitrogen content in the simulated coking wastewater prepared in Example 1 was measured to be 204.325mg / L.

[0074] The method for determining the total nitrogen content in the simulated coking wastewater prepared in Example 1 in Comparative Example 10 includes the following steps:

[0075] Dissolve 4.0 g of potassium persulfate (nitrogen content less than 0.0005%) in 60 mL of water (it can be heated in a 50 °C water bath until completely dissolved) to obtain a potassium persulfate solution;

[0076] Dissolve 1.5g of sodium hydroxide (containing less than 0.0005% nitrogen) in 30mL of water. After the sodium hydroxide solution cools to room temperature, a sodium hydroxide solution is obtained.

[0077] Mix potassium persulfate solution and sodium hydroxide solution, and then dilute to 100 mL to obtain an alkaline potassium persulfate solution.

[0078] After potassium nitrate was dried at 105-110℃ for 2 hours (the drying temperature in this example was 110℃), an appropriate amount was taken and dissolved in deionized water to prepare a series of total nitrogen standard solutions with different concentrations of 0 mg / L, 2 mg / L, 5 mg / L, 8 mg / L, 10 mg / L, 12.5 mg / L, 16 mg / L and 20 mg / L.

[0079] Take 1.00 mL of the total nitrogen standard solutions of different concentrations, add 3.0 mL of deionized water, place them in a 10 mL digestion tube, add 3.0 mL of alkaline potassium persulfate solution, seal the tube, and place it in a microwave digestion oven. Digest at 125℃ and 1200W for 30 min. Cool to room temperature, add 1 mL of disodium chromotropic acid solution (equivalent to 0.01 g disodium chromotropic acid) to the digestion solution, seal the tube tightly, shake vigorously up and down for 30 s, and let stand for 3 min. Transfer 2 mL of the resulting reaction solution to a colorimetric tube, slowly add 8 mL of sulfuric-phosphoric acid mixture, seal the tube tightly, invert the tube 10 times, cool in water for 10 min, and let stand at room temperature for 10 min. Under a strongly acidic environment, nitrate ions and chromotropic acid undergo a nitration reaction to produce a yellow nitrated product. Using water as a reference, the absorbance was measured at 410 nm using a visible spectrophotometer. The absorbance of the nitration products prepared with different concentrations of total nitrogen standard solutions was measured at 410 nm using visible spectrophotometry. An alkaline potassium persulfate-total nitrogen standard curve was plotted. (See attached image.) Figure 2 ;

[0080] Take 1.00 mL of the simulated coking wastewater prepared in Example 1, add 3.0 mL of deionized water, place it in a 10 mL digestion tube, then add 3.0 mL of alkaline potassium persulfate solution, seal the tube, and place it in a microwave digestion furnace. Digest at 125°C and 1200 W for 30 min. Cool to room temperature, add 1 mL of disodium chromotropic acid solution (equivalent to 0.01 g disodium chromotropic acid) to the digestion solution, tighten the lid, shake vigorously up and down for 30 s, let stand for 3 min, transfer 2 mL of the resulting reaction solution to a colorimetric tube, slowly add 8 mL of sulfuric-phosphoric acid mixture, tighten the lid, invert 10 times, cool in water for 10 min, and let stand at room temperature for 10 min. Under a strongly acidic environment, nitrate ions and chromotropic acid undergo nitration reaction to generate yellow nitration products. The standard curve of total nitrogen is plotted in this way, and alkaline potassium persulfate is no longer used as a digestion reagent to re-plot the standard curve. Using water as a reference, the absorbance of the nitration product prepared from the imitation coking wastewater was measured at 410 nm using a visible spectrophotometer. The absorbance was then calculated by substituting the absorbance into the alkaline potassium persulfate-total nitrogen standard curve. The total nitrogen content in the imitation coking wastewater was found to be 243.869 mg / L.

[0081] In Comparative Example 11, the total nitrogen content in the simulated coking wastewater prepared in Example 1 was determined using a rapid digestion method with alkaline potassium persulfate and ultraviolet spectrophotometry. The specific method included the following steps:

[0082] Take 0.7218g of potassium nitrate dried at 110℃ for 2h, dissolve it in an appropriate amount of water, transfer it to a 1000mL volumetric flask, dilute it with water to the mark, mix well, and obtain potassium nitrate stock solution.

[0083] Measure 10 mL of potassium nitrate stock solution into a 100 mL volumetric flask, dilute with water to the mark, mix well, and obtain potassium nitrate standard solution;

[0084] A series of different volumes of potassium nitrate standard solution, 0.00, 0.20, 0.50, 1.00, 2.00, 3.00, 4.00, and 5.00 mL, were measured into total nitrogen digestion tubes, corresponding to total nitrogen (N) contents of 0.00, 2.00, 5.00, 10.0, 20.0, 30.0, 40.0, and 50.0 μg, respectively. The solutions were diluted with water to 5.00 mL, and then 2.50 mL of alkaline potassium persulfate solution was added. (Prepared in the same manner as the alkaline potassium persulfate solution in Comparative Example 8), tighten the stopper, place the digestion tube in the digester, digest at 122℃ for 40 min, allow to cool naturally, add 0.50 mL of 10 wt% hydrochloric acid solution to each digestion tube, stopper and mix well. Using a 10 mm quartz cuvette, measure the absorbance at wavelengths of 220 nm and 275 nm on a UV spectrophotometer, with deionized water as a reference. The corrected absorbance A of deionized water is... b Corrected absorbance A for other potassium nitrate standard solutions of different volumes s and absorbance difference A r Calculate according to formulas (I), (II) and (III).

[0085] Plot the total nitrogen (as N) content (μg) in different volumes of potassium nitrate standard solution on the x-axis (i.e., X), and the corresponding absorbance difference value A. r Plot the calibration curve for total nitrogen with the ordinate (Y) as the ordinate, see [reference]. Figure 3 The calibration curve for the obtained total nitrogen is Y = 0.0279X + 0.012, R0 2 =0.9998.

[0086] A b =A b220 -2A b275 (I)

[0087] A s =A s220 -2A s275 (II)

[0088] A r =A s -A b (III)

[0089] In the formula: A b —Corrected absorbance of deionized water;

[0090] A b220 —Absorbance of deionized water at a wavelength of 220 nm;

[0091] A b275 —Absorbance of deionized water at a wavelength of 275 nm;

[0092] A s —Corrected absorbance of potassium nitrate standard solutions of different volumes;

[0093] A s220 —Absorbance of different volumes of potassium nitrate standard solution at a wavelength of 220 nm;

[0094] A s275 —Absorbance of different volumes of potassium nitrate standard solution at a wavelength of 275 nm;

[0095] A r —The difference in absorbance between the absorbance corrected by different volumes of potassium nitrate standard solution and the absorbance corrected by deionized water.

[0096] Take 1.00 mL of the simulated coking wastewater prepared in Example 1, dilute it with deionized water to 5.00 mL, place it in a stoppered digestion tube, add 2.50 mL of alkaline potassium persulfate solution (prepared in the same way as the alkaline potassium persulfate solution in Comparative Example 8), tighten the stopper, place the digestion tube in a digester, digest at 122°C for 40 min, allow it to cool naturally, add 0.50 mL of 10 wt% hydrochloric acid solution to each digestion tube, stopper and mix well, use a 10 mm quartz cuvette, and measure its absorbance at wavelengths of 220 nm and 275 nm on a UV spectrophotometer with deionized water as a reference. The corrected absorbance A of the deionized water is... b Corrected absorbance A of imitation coking wastewater s 'and absorbance difference A' r The absorbance difference A corresponding to the simulated coking wastewater was calculated using formulas (I), (IV), and (V). r '.

[0097] A b =A b220 -2A b275 (I)

[0098] A s '=A s220 '-2A s275 (Ⅳ)

[0099] A r '=A s '-Ab (V)

[0100] In the formula: A b —Corrected absorbance of deionized water;

[0101] A b220 —Absorbance of deionized water at a wavelength of 220 nm;

[0102] A b275 —Absorbance of deionized water at a wavelength of 275 nm;

[0103] A s '——Corrected absorbance of imitation coking wastewater;'

[0104] A s220 —Imitating the absorbance of coking wastewater at a wavelength of 220nm;

[0105] A s275 — The absorbance of coking wastewater at a wavelength of 275 nm was simulated.

[0106] A r '——The difference in absorbance between the corrected absorbance of imitation coking wastewater and the corrected absorbance of deionized water.'

[0107] The absorbance difference A corresponding to the simulated coking wastewater r Substituting the total nitrogen into the calibration curve, it was calculated that 1.00 mL of the imitation coking wastewater contained 242.627 μg, which means that the total nitrogen content in the imitation coking wastewater measured using the method in Comparative Example 11 was 242.627 mg / L.

[0108] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for detecting total nitrogen content in coking wastewater, characterized in that, The detection method includes the following steps: 1) Prepare total nitrogen standard solutions of different concentrations using potassium nitrate; 2) Take total nitrogen standard solutions of different concentrations, add water, nano-ferric oxide and hydrogen peroxide, microwave digest, cool, separate nano-ferric oxide, filter again, add disodium chromolate and sulfuric acid mixed with phosphoric acid to the filtrate to carry out nitration reaction, produce yellow nitrated products, and then use visible spectrophotometry to measure the absorbance of the nitrated products corresponding to different concentrations of total nitrogen standard solutions at 410 nm. Plot the total nitrogen standard curve based on the total nitrogen concentration in the total nitrogen standard solutions of different concentrations and the absorbance of the corresponding nitrated products. 3) Take coking wastewater, add water, then add nano-ferric oxide and hydrogen peroxide, microwave digest, cool, separate the nano-ferric oxide, filter again, add disodium chromolate and sulfuric acid mixed with sulfuric acid and phosphoric acid to the filtrate in sequence to carry out nitration reaction, produce yellow nitrated products, then use visible spectrophotometry to measure the absorbance of the nitrated products prepared from coking wastewater at 410 nm, substitute the absorbance of the nitrated products corresponding to the coking wastewater into the standard curve of total nitrogen, and calculate the total nitrogen content in the coking wastewater.

2. The method for detecting total nitrogen content in coking wastewater according to claim 1, characterized in that, In step 2), the volume-to-weight ratio of total nitrogen standard solutions of different concentrations to nano-Fe3O4 is 1 mL: 0.003–0.005 g. In step 3), the volume-to-weight ratio of coking wastewater to nano-ferric oxide is 1 mL: 0.003–0.005 g.

3. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In step 2), the concentration of hydrogen peroxide is 30 wt%, and the volume ratio of total nitrogen standard solution of different concentrations to hydrogen peroxide is 1:0.4 to 0.

5. In step 3), the concentration of hydrogen peroxide is 30 wt%, and the volume ratio of coking wastewater to hydrogen peroxide is 1:0.4 to 0.

5.

4. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In step 2), the microwave digestion temperature is 80–90℃, the power is 1100–1200W, and the time is 8–10 min; In step 3), the microwave digestion temperature is 80-90℃, the power is 1100-1200W, and the time is 8-10min.

5. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In step 2), the volume-to-weight ratio of the filtrate prepared from the total nitrogen standard solution of different concentrations to disodium chromotropic acid is 1 mL: 0.01–0.012 g. In step 3), the volume-to-weight ratio of the filtrate prepared from the coking wastewater to disodium chromotropic acid is 1 mL: 0.01–0.012 g.

6. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In step 2), the standard curve for total nitrogen is y = 56.334x - 0.0019, R0 2 =0.9996.

7. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In step 2), the volume ratio of total nitrogen standard solutions of different concentrations to water is 1:3; In step 3), the volume ratio of coking wastewater to water is 1:

3.

8. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In steps 2) and 3), the sulfuric-phosphoric acid mixture is made by mixing sulfuric acid with a concentration of 98% and concentrated phosphoric acid with a concentration of ≥85% in a volume ratio of 6:

4.

9. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In steps 2) and 3), nano-ferric oxide is prepared by adding ferric sulfate and ferric chloride to water and then using ammonia as a co-precipitant.

10. The method for detecting total nitrogen content in coking wastewater according to claim 1 or 2, characterized in that, In steps 2) and 3), the nitration reaction is a reaction between nitrate ions in the filtrate and chromotropic acid under the action of a sulfuric-phosphoric acid mixture. The chemical reaction formula for the nitration reaction is as follows:

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