A method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater

Abstract

The invention discloses a method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, comprising the steps of: preparing a plurality of nitro-oxidant wastewater solutions; calculating the calibrated H 2 O 2 The theoretical volume dosage was 1.5, and H was added to each group of solutions in increasing amounts. 2 O 2 , a blank control group was set up; the concentrations of nitrate nitrogen, nitrite nitrogen and nitrite in the wastewater of the six groups before neutralization, as well as the concentrations of nitrate nitrogen and nitrite nitrogen in the wastewater after neutralization were determined by spectrophotometry; the corresponding curves were drawn according to the measured data, and the ionization degree of nitrite, the removal rate of nitrite (including nitrite) in the wastewater of the six groups before neutralization, and the removal rate of N 2 O 4 The conversion rate of nitrogen in H 2 O 2 The invention determines the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, and provides a theoretical basis for achieving the maximum nitrogen element conversion rate and nitrite removal rate.

Description

Technical Field

[0001] The invention relates to the technical field of nitro-oxidant wastewater treatment, and in particular to a method for verifying the dosage of hydrogen peroxide used for treating nitro-oxidant wastewater. Background Art

[0002] Nitro-oxidizers include nitrogen tetroxide, green nitrogen tetroxide, and red smoke nitric acid. Due to their good energy characteristics, they are widely used in two-component liquid propellant systems. Nitro-oxidizers are strong oxidizing acids. Leakage and loss accidents often occur during production, storage, transportation, or filling. A large amount of wastewater will be generated when dealing with such accidents. In addition, after completing the transfer task, a large amount of wastewater will be generated during the cleaning and disinfection of nitro-oxidizer storage tanks, tank trucks, pump trucks, and pipelines. This type of wastewater contains a large amount of nitrogen tetroxide oxidizer, which is generally neutralized with 3% to 5% sodium carbonate solution and then rinsed with a large amount of tap water. The wastewater can be directly discharged when the pH value reaches 6.5 to 8.5.

[0003] The main components of treated sewage are sodium nitrate (NaNO3), sodium nitrite (NaNO2) and sodium carbonate (Na2CO3), but the water still contains a large amount of NO2 - After nitrite is discharged, it is easy to dissolve in groundwater, exceeding the surface water discharge standard. If it is consumed for a long time, it may cause nitrite poisoning. Nitrite poisoning is also called enterogenic cyanosis. Nitrite is a strong oxidant under acidic conditions. After being absorbed by the human digestive tract and entering the blood circulation, it can increase the iron-low hemoglobin (Fe 2+ ) is oxidized to methemoglobin (Fe 3+ ), forming methemoglobinemia, which makes hemoglobin lose the function of transporting oxygen and oxygenating hemoglobin to release oxygen, resulting in tissue hypoxia, typical symptoms of cyanosis and poisoning. Due to hypoxia, the central nervous system will be damaged first, so symptoms such as headache, dizziness, nausea, vomiting, and weakness in the limbs will appear, and it often causes damage to multiple organs such as the heart, liver, brain, kidneys, and lungs. In addition, nitrite will directly dilate vascular smooth muscle, so hypotension may occur. Nitrite can also react with secondary or tertiary amines to form carcinogenic nitrosamines. Generally, areas with high nitrite content in drinking water also have high incidence of gastric cancer.

[0004] In the treatment process of nitro-oxidant wastewater, based on the unstable characteristics of nitrogen atoms in nitrite, which are both reducing and oxidizing, a strong reducing agent is usually added to reduce nitrite to low-valent nitrogen oxides or nitrogen element, or an oxidizing agent with stronger oxidizing ability than nitrite is added to oxidize it to nitrate. In the prior art article "Research on the Removal of Sodium Nitrite in Aquaculture Water [D]", iron powder, reduced iron powder, zinc powder, and thiourea dioxide were used as reducing agents to experiment on sodium nitrite. The results showed that zinc powder had the best removal effect, with a removal rate of only 43.76%, and the cost was relatively high. Using strong oxidants to oxidize NO2 - Ions make it NO3 - The advantages of ions are fast reaction speed, low cost and high oxidation efficiency, but in actual production, they also have the disadvantage that the amount used is difficult to control, that is, the effect of degrading nitrite at low concentration is not obvious, and high concentration will cause phytotoxicity. Air oxidation of low-concentration nitrite is an extremely slow process, while the use of hydrogen peroxide can efficiently treat high-concentration nitrite wastewater under mild conditions, and combined with distillation, crystallization and other steps, nitrate resource recovery can be achieved, which has certain economic benefits. However, how to determine the dosage of hydrogen peroxide at the optimal ratio to achieve the maximum nitrogen element conversion rate and nitrite removal rate has not been disclosed in the prior art. How to efficiently treat nitro-oxidant wastewater is a problem that needs to be solved. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, determines the optimal dosage of hydrogen peroxide added when treating nitro-oxidant wastewater, and provides a theoretical basis for achieving the maximum nitrogen element conversion rate and nitrite removal rate.

[0006] The technical solution adopted by the present invention to achieve the above technical effects is:

[0007] A method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater comprises the steps of:

[0008] S1. Prepare 6 groups of 1g nitrogen tetroxide / 100mL water nitro-oxidant wastewater solutions, numbered as group 1, group 2, group 3, group 4, group 5, and group 6;

[0009] S2. According to the stoichiometric relationship of the chemical reaction equation N2O4+H2O2=2HNO3, the theoretical volume dosage of H2O2 was calculated. Group 1 was set as the control group. H2O2 reagent with increasing dosage was added to groups 2, 3, 4, 5, and 6, respectively, and recorded as W. i , where W1 = 0 mL;

[0010] S3. Use spectrophotometry to determine the corresponding absorbance value and calculate the concentration of nitrate nitrogen in the 6 groups of wastewater before neutralization. Ai 、Concentration of nitrite nitrogen c Bi , pH value (pH) i 、Concentration of nitrite c(HNO2) i , and the concentration of nitrate nitrogen in the wastewater after neutralization c ai 、Concentration of nitrite nitrogen c bi ;

[0011] S4, draw a curve chart of the corresponding change rule according to the data measured in step S3, and calculate the ionization degree β of nitrite in the 6 groups of wastewater before neutralization respectively. i 、Removal rate of nitrite (including nitrous acid) Z i , and the conversion rate of nitrogen in N2O4 after neutralization Y i ;

[0012] S5. According to the data in step S4, the optimal dosage of H2O2 is determined as: 20% excess over the theoretical dosage.

[0013] Preferably, the preparation process of the nitro-oxidant wastewater solution in step S1 is:

[0014] S11, keep the blown ampoule ball in a constant temperature balance room for 30 minutes, weigh its mass, and record it as m0;

[0015] S12. Fill each ampoule ball with 1g of liquid nitrogen tetroxide (N2O4) by syringe sampling method, immediately seal the tube mouth, put it in the balance room and keep it at a constant temperature for 30 minutes, weigh the mass of the ampoule ball filled with the sample, record it as m i ;

[0016] S13. Gently slide the ampoule ball from the mouth of the 250mL stoppered conical bottle to the bottom of the bottle. The amount of water in the conical bottle is determined according to the mass of the N2O4 sample in the ampoule ball, so that every 100mL of distilled water contains 1g of N2O4 sample. The volume of water added is recorded as U i ;

[0017] S14. When using, break the ampoule ball to dissolve the N2O4 in it into the distilled water in the conical flask.

[0018] Preferably, it also includes the establishment of a nitrate nitrogen standard working curve y1 and a nitrite nitrogen standard working curve y2, wherein the nitrate nitrogen standard working curve y1 is specifically: y1=0.25442x1, and the correlation coefficient is R 2 =0.99997; the standard working curve of nitrite nitrogen y2 is specifically: y2=0.05012x2, and the correlation coefficient is R 2 =0.99951.

[0019] Preferably, the concentration of nitrate nitrogen in the wastewater before neutralization is c Ai The determination process is as follows: after adding H2O2 in step S2, the wastewater is left to stand for a certain period of time, and after the nitrite and nitrite ions in the wastewater fully react with H2O2, the supernatant volume V is immediately removed with a pipette. A , nitrate nitrogen concentration was determined by spectrophotometry.

[0020] Preferably, the neutralization is to add 2 drops of phenolphthalein indicator solution (unit: 10 g / L) to the wastewater solution, and titrate with a calibrated NaOH solution until the solution turns pink and remains unfaded for 30 seconds, and at the same time do a control test, and record the actual concentration of the calibrated sodium hydroxide solution as Its unit is mol / L, and the volume of NaOH solution consumed is recorded as V i , the volume of NaOH solution consumed in the control experiment is recorded as V1.

[0021] Preferably, the concentration of nitrite nitrogen in the wastewater before neutralization is c Bi The calculation formula is:

[0022] C Bi =10 -(pH)i -C Ai ;

[0023] Where, (pH) i It is the pH value of nitro-oxidant wastewater before neutralization.

[0024] Preferably, the concentration of nitrite in the wastewater before neutralization is c(HNO2) i The calculation formula is:

[0025]

[0026] Where U i The volume of water added to prepare a nitro-oxidant wastewater solution of 1 g nitrogen tetroxide / 100 mL water, W i is the amount of hydrogen peroxide reagent input in step S2.

[0027] Preferably, the degree of ionization of nitrous acid in the wastewater before neutralization is β i The calculation formula is:

[0028]

[0029] Preferably, the removal rate Z of nitrite (containing nitrous acid) in the wastewater before neutralization is i The calculation formula is:

[0030]

[0031] Preferably, the conversion rate of nitrogen in N2O4 after neutralization is Y i The calculation formula is:

[0032]

[0033] The beneficial effects of the present invention are as follows: the present invention uses hydrogen peroxide as an oxidant to explore its oxidation effect on nitrite, and through practical verification, determines the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, providing a theoretical basis for achieving the maximum nitrogen element conversion rate and nitrite removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the present invention;

[0035] Figure 2 The results of 6 groups of different H2O2 dosages are shown in Table 1. Ai The changing law curve diagram of

[0036] Figure 3 The results of 6 groups of different H2O2 dosages are shown in Table 1. ai The changing law curve diagram of

[0037] Figure 4 The results of 6 groups of different H2O2 dosages are shown in Table 1. bi The changing law curve diagram of

[0038] Figure 5 The curve diagram of pH value variation under 6 groups of different H2O2 dosages;

[0039] Figure 6 The results of 6 groups of different H2O2 dosages are shown in Table 1. Bi The changing law curve diagram of

[0040] Figure 7 c(HNO2) for 6 groups with different H2O2 dosage i The changing law curve diagram of

[0041] Figure 8 The ionization degree β under 6 different H2O2 dosages i Histogram of ;

[0042] Fig. 9 is the nitrogen conversion rate Y under 6 different H2O2 dosages i Line chart of

[0043] Fig.10 This is the ED curve diagram of the present invention. DETAILED DESCRIPTION

[0044] In order to further understand the present invention, the present invention is further described below with reference to the figures and specific embodiments:

[0045] like Figure 1 As shown, the present invention discloses a method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, which comprises the steps of:

[0046] S1. Prepare 6 groups of 1g nitrogen tetroxide / 100mL water nitro-oxidant wastewater solutions, numbered as group 1, group 2, group 3, group 4, group 5, and group 6;

[0047] S2. According to the stoichiometric relationship of the chemical reaction equation N2O4+H2O2=2HNO3, the theoretical volume dosage of H2O2 was calculated. Group 1 was set as the control group. H2O2 reagent with increasing dosage was added to groups 2, 3, 4, 5, and 6, respectively, and recorded as W. i , where W1 = 0 mL;

[0048] S3. Use spectrophotometry to determine the corresponding absorbance value and calculate the concentration of nitrate nitrogen in the 6 groups of wastewater before neutralization. Ai 、Concentration of nitrite nitrogen c Bi , pH value (pH) i 、Concentration of nitrite c(HNO2) i , and the concentration of nitrate nitrogen in the wastewater after neutralization c ai 、Concentration of nitrite nitrogen c bi ;

[0049] S4, draw a curve chart of the corresponding change rule according to the data measured in step S3, and calculate the ionization degree β of nitrite in the 6 groups of wastewater before neutralization respectively. i 、Removal rate of nitrite (including nitrous acid) Z i , and the conversion rate of nitrogen in N2O4 after neutralization Y i ;

[0050] S5. According to the data in step S4, the optimal dosage of H2O2 is determined as: 20% excess over the theoretical dosage.

[0051] Specifically, the preparation process of the nitro-oxidant wastewater solution in step S1 is:

[0052] S11, keep the blown ampoule ball in a constant temperature balance room for 30 minutes, weigh its mass, and record it as m0;

[0053] S12. Fill each ampoule ball with 1g of liquid nitrogen tetroxide (N2O4) by syringe sampling method, immediately seal the tube mouth, put it in the balance room and keep it at a constant temperature for 30 minutes, weigh the mass of the ampoule ball filled with the sample, record it as m i ;

[0054] S13. Gently slide the ampoule ball from the mouth of the 250mL stoppered conical bottle to the bottom of the bottle. The amount of water in the conical bottle is determined according to the mass of the N2O4 sample in the ampoule ball, so that every 100mL of distilled water contains 1g of N2O4 sample. The volume of water added is recorded as U i ;

[0055] S14. When using, break the ampoule ball to dissolve the N2O4 in it into the distilled water in the conical flask.

[0056] It also includes the establishment of a nitrate nitrogen standard working curve y1 and a nitrite nitrogen standard working curve y2. Specifically, the nitrate nitrogen standard working curve y1 is: y1 = 0.25442x1, and the correlation coefficient is R 2 =0.99997; the standard working curve of nitrite nitrogen y2 is specifically: y2=0.05012x2, and the correlation coefficient is R 2 =0.99951.

[0057] The concentration of nitrate nitrogen in wastewater before neutralization c Ai The determination process is as follows: after adding H2O2 in step S2, let it stand for a certain period of time, and after the nitrite and nitrite ions in the wastewater fully react with H2O2, immediately use a pipette to remove the supernatant volume V A The nitrate nitrogen concentration was determined by spectrophotometry. Neutralization was performed by adding 2 drops of phenolphthalein indicator solution (10 g / L) to the wastewater solution, titrating with a calibrated NaOH solution until the solution turned pink and remained pink for 30 seconds. A control test was performed at the same time, and the actual concentration of the calibrated sodium hydroxide solution was recorded as Its unit is mol / L, and the volume of NaOH solution consumed is recorded as V i , the volume of NaOH solution consumed in the control experiment is recorded as V1.

[0058] The concentration of nitrite nitrogen in wastewater before neutralization c Bi The calculation formula is:

[0059] C Bi =10 -(pH)i -C Ai ;

[0060] Where, (pH) i It is the pH value of nitro-oxidant wastewater before neutralization.

[0061] Concentration of nitrite in wastewater before neutralization c(HNO2) i The calculation formula is:

[0062]

[0063] Where U iThe volume of water added to prepare a nitro-oxidant wastewater solution of 1 g nitrogen tetroxide / 100 mL water, W i is the amount of hydrogen peroxide reagent input in step S2.

[0064] Ionization degree of nitrite in wastewater before neutralization β i The calculation formula is:

[0065]

[0066] Removal rate Z of nitrite (including nitrous acid) in wastewater before neutralization i The calculation formula is:

[0067]

[0068] The conversion rate of nitrogen in N2O4 after neutralization is Y i The calculation formula is:

[0069]

[0070] Below, the present invention is described in detail in conjunction with specific experimental data:

[0071] Each group of nitro-oxidant wastewater solution was prepared in 5 portions, and 5 parallel experiments with the same experimental steps were carried out. Numbers 1-6, 7-12, 13-18, 19-24, 25-30 correspond to the 1st, 2nd, 3rd, 4th, and 5th groups of experiments, respectively. Group 1 was set as a control experiment, that is, no H2O2 reagent was added to the conical flask, the amount of H2O2 in group 2 was the theoretical amount, the amount of H2O2 in group 3 was added at 10% excess of the theoretical amount, the amount of H2O2 in group 4 was added at 20% excess of the theoretical amount, the amount of H2O2 in group 5 was added at 50% excess of the theoretical amount, and the amount of H2O2 in group 6 was added at 80% excess of the theoretical amount. The volume amounts of H2O2 were recorded as W2, W3, W4, W5, and W6, respectively.

[0072] Shake the ampoule ball in the conical flask to release the N2O4, shake it for 5 seconds and let it stand for 1 hour. After the reaction is complete, immediately use a pipette to remove the supernatant volume V A For spectrophotometric determination of nitrate nitrogen content

[18] Then add 2 drops of phenolphthalein indicator solution (10 g / L) to each conical flask, and titrate with the calibrated NaOH solution until the solution turns pink and remains pink for 30 seconds. This is the end point, and a control test is performed at the same time. The volume of NaOH solution consumed by the sample solution is recorded as V i , the volume of NaOH solution consumed in the control experiment is recorded as V1.

[0073] After the titration is completed, let it stand for 1 min and take the supernatant V with a pipette. aFor spectrophotometric determination of nitrate nitrogen absorbance, take the supernatant V b It is used to determine the absorbance of nitrite nitrogen by spectrophotometry and then calculate the concentration of nitrate nitrogen and nitrite nitrogen. To improve the accuracy of the experimental results, five parallel experiments with the same experimental steps were conducted, and the numbers 1-6, 7-12, 13-18, 19-24, and 25-30 correspond to the 1st, 2nd, 3rd, 4th, and 5th groups of experiments, respectively.

[0074] The nitrate nitrogen absorbance was determined by spectrophotometry, and the concentration of nitrate nitrogen in the wastewater before neutralization was calculated. Ai , unit mol / L. Specifically, the calculation formula for the nitrate nitrogen concentration in the nitro-oxidant wastewater before neutralization is as follows:

[0075]

[0076] Where: i is the corresponding conical flask number, i = 1, 2, 3, 4, 5, 6; A i is the absorbance value of nitrate nitrogen before neutralization; ρA is the content of nitrate nitrogen standard solution, ρ A =0.1 mg / mL; K is the slope of the nitrate nitrogen standard working curve y1; V A The volume of nitro-oxidant wastewater removed before neutralization, V A It is set to a fixed value, which is 0.05 mL in the embodiment of the present invention; M is the relative atomic mass of the nitrogen atom, M=14 g / mol.

[0077] The unit of nitrate nitrogen concentration in the nitro-oxidant wastewater after neutralization is mol / L, and the calculation formula is as follows:

[0078]

[0079] Where: A i ′ is the absorbance value of nitrate nitrogen after neutralization; V a V is the volume of nitro-oxidant wastewater removed after neutralization. a It is set to a fixed value, which is 0.05 mL in the embodiment of the present invention.

[0080] Nitrite nitrogen concentration in nitro-oxidant wastewater after neutralization c bi The unit is mol / L, and the calculation formula is as follows:

[0081]

[0082] Where: B i ' is the absorbance value of nitrite nitrogen after neutralization; ρ B is the nitrite nitrogen content of the standard solution, ρ B =1μg / mL; k is the slope of the nitrite nitrogen standard working curve y2; V bV is the volume of nitro-oxidant wastewater removed after neutralization. b It is set to a fixed value, which is 0.03 mL in the embodiment of the present invention.

[0083] Specifically, the nitrite nitrogen concentration in the nitro-oxidant wastewater before neutralization is c Bi The calculation process is:

[0084] Before the nitro-oxidant wastewater is neutralized, there is charge conservation in the solution. Assuming the concentration of free hydrogen ions in the solution is c(H + ) i , the unit is mol / L, the nitrite nitrogen concentration of nitro-oxidant wastewater before neutralization is c Bi , the unit is mol / L, then the following relationship exists:

[0085] c(H + ) i =c Ai +c Bi ;

[0086] Among them, c(H + ) can be calculated from the pH value of the nitro-oxidant wastewater before neutralization, that is, there is:

[0087]

[0088] From the above two equations, we can get the nitrite nitrogen concentration c in the nitrate oxidant wastewater before neutralization: Bi The calculation formula is:

[0089] C Bi =10 -(pH)i -C Ai .

[0090] The calculation process of nitrite concentration in nitro-oxidant wastewater before neutralization is:

[0091] There are three main forms of nitrogen in the solution before neutralization, namely nitrite, nitrate, and nitrous acid molecules. According to the conservation of nitrogen material, assuming that the concentration of nitrous acid in the solution is c(HNO2)i, in mol / L, the following relationship exists:

[0092]

[0093] The calculation process of nitrite ionization degree in nitro-oxidant wastewater before neutralization is:

[0094] Knowing the concentration of nitrite and nitrous acid molecules in the solution before neutralization, we can also calculate the actual ionization degree of nitrous acid in the solution. Assuming the ionization degree is βi (%), we have:

[0095]

[0096] The calculation process of nitrogen conversion rate in nitro-oxidant wastewater after neutralization is:

[0097] The conversion rate of nitrogen in nitrogen tetroxide can be analyzed in this way. A part of nitrogen escapes in the form of nitrogen oxide gas. We can use the existence of various nitrogen in the solution to calculate the total nitrogen concentration in the solution, and the theoretical concentration of nitrogen can be considered as the nitrogen concentration in nitrogen tetroxide. The ratio of the two is the nitrogen conversion rate. Taking the neutralized nitro-oxidant wastewater as an example, assuming that the conversion rate of nitrogen in nitrogen tetroxide is Y i (%), the total nitrogen concentration in the nitro-oxidant wastewater after neutralization is c(N)i, in mol / L, and the theoretical concentration of nitrogen is c(L)i, in mol / L. The following relationship exists among the three:

[0098]

[0099] Where c(N)i and c(L)i satisfy the following relationships respectively:

[0100] c(N) i =c ai +c bi ;

[0101]

[0102] From the above three equations, we can get Y i The final expression of is:

[0103]

[0104] The calculation process of nitrite removal rate in nitro-oxidant wastewater before neutralization is:

[0105] In order to investigate the destination of nitrite in solution and study the change law of nitrite in solution, the concept of removal rate is introduced here, that is, to study the actual conversion rate of nitrite (including nitrite) from the beginning of nitrogen tetroxide being put into water to the full reaction in solution. Suppose the removal rate of nitrite (including nitrite) is Z i (%), the expression of nitrite removal rate is as follows:

[0106]

[0107] The following lists the measurement data and result processing table as well as the relevant inspection process:

[0108] Among them, c Ai 、c ai 、c bi The calculation results are shown in Table 1 below:

[0109] Table 1c Ai 、cai 、c bi Calculation results

[0110]

[0111]

[0112] like Figures 2 to 5 As shown, they are 6 groups of c under different H2O2 dosages. Ai The changing law curve of c ai The changing law curve of c bi The change curve of pH value. Figures 2 to 5 The data analysis of Table 1 is as follows:

[0113] (1)c Ai With c ai When the H2O2 feed amount does not exceed 1.1 times the theoretical amount, as the H2O2 feed amount increases, c Ai 、c ai It is also increasing. When the H2O2 feed amount exceeds 1.1 times the theoretical feed amount, c Ai 、c ai This indicates that the addition of H2O2 can change the content of nitrate nitrogen in wastewater to a certain extent, but excessive addition is not conducive to the actual conversion of nitrate ions, because the decomposition tendency of excess H2O2 itself is enhanced, and the actual oxidation efficiency is reduced.

[0114] (2) The nitrite nitrogen concentration of nitro-oxidant wastewater that has not been treated with H2O2 is nearly 3 times higher than that of the treated wastewater. The main reason is that H2O2 has a strong oxidizing property and can oxidize nitrite or nitrous acid into nitrate. When the H2O2 feed amount is 1.2 times the theoretical feed amount, c bi It drops to the lowest level, indicating that H2O2 at this feed ratio is beneficial to the maximum oxidation of nitrite generated in the solution.

[0115] (3) Regardless of whether H2O2 is added or not, the pH value of the wastewater is lower than 0.826. Adding H2O2 can also reduce the pH value of the solution to a certain extent. The main reason is that H2O2 oxidizes some of the undissociated nitrite molecules into nitric acid, making H + It is released, increasing the acidity of the solution and lowering the pH value of the solution.

[0116] Among them, c Bi 、c(HNO2) i 、c(N) i 、c(L) i , Y iThe calculation results are shown in Table 2 below:

[0117] Table 2c Bi 、c(HNO2) i 、c(N) i 、c(L) i , Y i Calculation results table

[0118] serial number <![CDATA[c Bi / mol·L -1 ]]> <![CDATA[c(HNO2) i / mol·L -1 ]]> <![CDATA[β i / %]]> <![CDATA[c(N) i / mol·L -1 ]]> <![CDATA[c(L) i / mol·L -1 ]]> <![CDATA[Y i / %]]> 1 <![CDATA[1.5677×10 -5 ]]> <![CDATA[3.3537×10 -3 ]]> 0.465 0.1343 0.1880 71.41 2 <![CDATA[3.2223×10 -6 ]]> <![CDATA[9.5392×10 -4 ]]> 0.337 0.1742 0.1771 98.35 3 <![CDATA[3.0855×10 -6 ]]> <![CDATA[9.2575×10 -4 ]]> 0.332 0.1761 0.1765 99.78 4 <![CDATA[2.8778×10 -6 ]]> <![CDATA[8.6270×10 -4 ]]> 0.332 0.1759 0.1763 99.79 5 <![CDATA[3.1759×10 -6 ]]> <![CDATA[9.4690×10 -4 ]]> 0.334 0.1752 0.1758 99.66 6 <![CDATA[3.2293×10 -6 ]]> <![CDATA[9.5633×10 -4 ]]> 0.337 0.1742 0.1753 99.37 7 <![CDATA[1.5569×10 -5 ]]> <![CDATA[3.3538×10 -3 ]]> 0.462 0.1351 0.1879 71.90 8 <![CDATA[3.2252×10 -6 ]]> <![CDATA[9.5393×10 -4 ]]> 0.337 0.1740 0.1771 98.26 9 <![CDATA[3.0854×10 -6 ]]> <![CDATA[9.2575×10 -4 ]]> 0.332 0.1761 0.1765 99.79 10 <![CDATA[2.8781×10 -6 ]]> <![CDATA[8.6271×10 -4 ]]> 0.333 0.1759 0.1763 99.78 11 <![CDATA[3.1738×10 -6 ]]> <![CDATA[9.4625×10 -4 ]]> 0.334 0.1752 0.1758 99.66 12 <![CDATA[3.2273×10 -6 ]]> <![CDATA[9.5638×10 -4 ]]> 0.336 0.1743 0.1753 99.43 13 <![CDATA[1.5845×10 -5 ]]> <![CDATA[3.3590×10 -3 ]]> 0.469 0.1333 0.1883 70.78 14 <![CDATA[3.2516×10 -6 ]]> <![CDATA[9.6462×10 -4 ]]> 0.336 0.1745 0.1770 98.56 15 <![CDATA[3.0460×10 -6 ]]> <![CDATA[9.1400×10 -4 ]]> 0.332 0.1761 0.1765 99.79 16 <![CDATA[2.8238×10 -6 ]]> <![CDATA[8.4648×10 -4 ]]> 0.332 0.1759 0.1763 99.78 17 <![CDATA[3.2110×10 -6 ]]> <![CDATA[9.5739×10 -4 ]]> 0.334 0.1752 0.1758 99.67 18 <![CDATA[3.2870×10 -6 ]]> <![CDATA[9.7478×10 -4 ]]> 0.336 0.1744 0.1753 99.51 19 <![CDATA[1.5174×10 -5 ]]> <![CDATA[3.2453×10 -3 ]]> 0.465 0.1342 0.1881 71.34 20 <![CDATA[3.1850×10 -6 ]]> <![CDATA[9.4093×10 -4 ]]> 0.337 0.1739 0.1772 98.14 21 <![CDATA[3.0496×10 -6 ]]> <![CDATA[9.1505×10 -4 ]]> 0.332 0.1761 0.1765 99.78 22 <![CDATA[2.9279×10 -6 ]]> <![CDATA[8.7763×10 -4 ]]> 0.333 0.1759 0.1763 99.79 23 <![CDATA[3.1602×10 -6 ]]> <![CDATA[9.4222×10 -4 ]]> 0.334 0.1752 0.1758 99.66 24 <![CDATA[3.1786×10 -6 ]]> <![CDATA[9.4178×10 -4 ]]> 0.336 0.1743 0.1753 99.41 25 <![CDATA[1.5278×10 -5 ]]> <![CDATA[3.2192×10 -3 ]]> 0.472 0.1325 0.1884 70.30 26 <![CDATA[3.1704×10 -6 ]]> <![CDATA[9.3979×10 -4 ]]> 0.336 0.1743 0.1770 98.47 27 <![CDATA[2.9411×10 -6 ]]> <![CDATA[8.8263×10 -4 ]]> 0.332 0.1761 0.1765 99.79 28 <![CDATA[2.9444×10 -6 ]]> <![CDATA[8.8254×10 -4 ]]> 0.333 0.1759 0.1763 99.79 29 <![CDATA[3.0139×10 -6 ]]> <![CDATA[8.9888×10 -4 ]]> 0.334 0.1752 0.1758 99.67 30 <![CDATA[3.0815×10 -6 ]]> <![CDATA[9.1293×10 -4 ]]> 0.336 0.1742 0.1753 99.38

[0119] like Figures 6 to 9 As shown, they are 6 groups of c under different H2O2 dosages. Bi The changing curve of c(HNO2) i The changing curve of ionization degree β i Histogram of nitrogen conversion rate Y i Line chart of . Combined curve Figures 6 to 9 The data analysis of Table 2 is as follows:

[0120] (1) The addition of H2O2 can significantly reduce the concentration of nitrite molecules and nitrite ions, and when the H2O2 feed amount is 1.2 times the theoretical feed amount, c Bi and c(HNO2) i In addition, compared with c Bi and c(HNO2) i The value of HNO2 in wastewater shows that the concentration of HNO2 is higher than that of NO2 - It is much larger, indicating that trivalent nitrogen mainly exists in the solution in the form of HNO2 molecules, which is inseparable from the influence of the strong acidic environment. The stronger the acidity, the more it will inhibit the normal ionization of HNO2 molecules, resulting in a larger proportion of free molecules in the solution.

[0121] (2) The actual ionization degree of nitrite molecules does not exceed 0.5%, and more than 99.5% exists in the solution in molecular form. In addition, the ionization degree of the control test (without adding H2O2) is slightly higher than that of other groups. This is because the pH value of the control test is higher than that of other groups, which promotes the ionization of nitrite in the positive direction, making the ionization degree slightly higher.

[0122] (3) When no H2O2 was added, the nitrogen conversion rate was only 71.15%. After H2O2 was added according to the stoichiometric ratio, the nitrogen conversion rate increased significantly. When the H2O2 content just reached the stoichiometric ratio, the nitrogen conversion rate rapidly increased to 98.4%. When the H2O2 content was 10% in excess, the nitrogen conversion rate still increased slightly, reaching 99.79%. However, as the H2O2 dosage ratio continued to increase, the nitrogen conversion rate gradually decreased. The reason is that the H2O2 concentration is too high, the tendency of intermolecular collision increases, the H2O2 decomposition rate increases, and its effective utilization rate decreases. Under the premise of maintaining a high nitrogen conversion rate, H2O2 can meet the demand by 10% to 20% in excess of the theoretical amount, without excessive addition, to avoid excessive loss of H2O2.

[0123] Among them, c Ai and c bi The data reliability test process is as follows:

[0124] There is a nitrogen balance in the solution before neutralization. The amount of nitrogen substance is analyzed. Although we don’t know how much nitrogen tetroxide in the wastewater is converted into nitric acid and nitrous acid, according to the law of conservation of materials, it can be concluded that the amount of total nitrogen in the solution is equal to the total amount of hydrogen ions consumed by sodium hydroxide. The total amount of hydrogen ions is expressed as n(H). i (mol) (excluding undissociated H2O molecules), the following equivalent relationship is obtained from the conservation of materials:

[0125]

[0126] n(H) i It can be calculated from the amount of NaOH consumed in the acid-base neutralization reaction, that is, the following relationship exists:

[0127]

[0128] From the above two formulas, we can calculate c Ai and c bi The following relationship exists:

[0129]

[0130] This formula is used as a test c Ai and c bi The important basis of data reliability, for the convenience of expression, let D i =c Ai (U i +W i )+c bi (U i +W i +V i ), The relevant calculation results are shown in Table 3 below:

[0131] Table 3D i 、E i Calculation results table

[0132]

[0133]

[0134] In order to study the correlation between the two sets of data D and E, a working curve y=x is established with E as the ordinate and D as the abscissa. Fig. 9 As shown, the fitting curve is a straight line that just passes through the origin, and the linear correlation is R 2 =1, indicating that the two sets of data are highly consistent and satisfy the above equation.

[0135] In order to make the reaction proceed quickly and completely, it is necessary to understand the optimal feed ratio of the reaction. For this reason, we calculated the theoretical dosage of hydrogen peroxide according to the amount of nitrogen tetroxide added, and determined the dosage of hydrogen peroxide according to no addition, just reaction, 10% excess, 20% excess, 50% excess, and 80% excess. After fully reacting for 1 hour and after neutralization reaction, the concentration of nitrite nitrogen in the solution was measured and calculated, and the removal rate of nitrite ion was finally obtained, as shown in Table 4 below:

[0136] Table 4 Removal rate of nitrite under different hydrogen peroxide addition ratios

[0137]

[0138] As can be seen from Table 4, even if nitrogen tetroxide is directly added to water (1gN2O4 / 100mL water), the removal rate of nitrite is 98.47%, which shows that nitrite cannot exist in large quantities and stably in acidic aqueous solution. Most of the nitrite is immediately decomposed and converted into nitrate. By simple calculation, nitrite accounts for less than 2.2% of nitrogen in the solution (less than 0.5% when hydrogen peroxide is added), which further illustrates the instability of nitrite in acidic environment. At the same time, it can be seen from the table that when the amount of hydrogen peroxide added is 20% more than the theoretical amount, the nitrite removal rate reaches the highest (99.60%). However, it is not the case that the higher the hydrogen peroxide content, the higher the nitrite removal rate. This is because hydrogen peroxide is not conducive to its stable existence under strong acid or strong alkali conditions, and its decomposition rate is accelerated. The excessive concentration of hydrogen peroxide increases its own decomposition reaction, which reduces its effective utilization rate. From the discussion on comprehensive nitrogen conversion rate and nitrite removal rate, it can be seen that the dosage of hydrogen peroxide should be 20% excess of the theoretical amount.

[0139] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions only describe the principles of the present invention. The present invention may have various changes and improvements without departing from the spirit and scope of the present invention, and these changes and improvements fall within the scope of the present invention to be protected, and the scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater, characterized in that: Includes steps: S1. Prepare 6 groups of 1g nitrogen tetroxide / 100mL water nitro-oxidant wastewater solutions, numbered as group 1, group 2, group 3, group 4, group 5, and group 6; S2. According to the stoichiometric relationship of the chemical reaction equation N2O4+H2O2=2HNO3, the theoretical volume dosage of H2O2 was calculated. Group 1 was set as the control group. H2O2 reagent with increasing dosage was added to groups 2, 3, 4, 5, and 6, respectively, and recorded as W. i , where W1 = 0 mL; S3. Use spectrophotometry to determine the corresponding absorbance value and calculate the concentration of nitrate nitrogen in the 6 groups of wastewater before neutralization. Ai 、Concentration of nitrite nitrogen c Bi , pH value (pH) i 、Concentration of nitrite c(HNO2) i , and the concentration of nitrate nitrogen in the wastewater after neutralization c ai 、Concentration of nitrite nitrogen c bi ; Among them, the nitrate nitrogen concentration in the nitro-oxidant wastewater before neutralization is c Ai The calculation formula is as follows: Where: i is the corresponding conical flask number, i = 1, 2, 3, 4, 5, 6; A i is the absorbance value of nitrate nitrogen before neutralization; ρ A is the nitrate nitrogen standard solution content, ρ A =0.1 mg / mL; K is the slope of the nitrate nitrogen standard working curve y1; V A The volume of nitro-oxidant wastewater removed before neutralization, V A＝ 0.05mL; M is the relative atomic mass of nitrogen atom, M = 14g / mol; Nitrate nitrogen concentration in nitro-oxidant wastewater after neutralization c ai The unit is mol / L, and the calculation formula is as follows: Where: A i ′ is the absorbance value of nitrate nitrogen after neutralization; V a V is the volume of nitro-oxidant wastewater removed after neutralization. a＝ 0.05mL; Nitrite nitrogen concentration in nitro-oxidant wastewater after neutralization c bi The unit is mol / L, and the calculation formula is as follows: Where: B i ' is the absorbance value of nitrite nitrogen after neutralization; ρ B is the nitrite nitrogen standard solution content, ρ B =1μg / mL; k is the slope of the nitrite nitrogen standard working curve y2; V b V is the volume of nitro-oxidant wastewater removed after neutralization. b＝ 0.03mL; Nitrite nitrogen concentration in nitro-oxidant wastewater before neutralization c Bi The calculation formula is as follows: C Bi =10 -(pH)i -C Ai ; Where: (pH) i The pH value of nitro-oxidant wastewater before neutralization; Nitrite concentration in nitro-oxidant wastewater before neutralization c(HNO2) i The calculation formula is as follows: Where: is the actual concentration of the calibrated sodium hydroxide solution, V i is the volume of NaOH solution consumed during calibration, U i The volume of water added to prepare a nitro-oxidant wastewater solution of 1 g nitrogen tetroxide / 100 mL water, W i is the input amount of hydrogen peroxide reagent in step S2; S4, draw a curve chart of the corresponding change rule according to the data measured in step S3, and calculate the ionization degree β of nitrite in the 6 groups of wastewater before neutralization respectively. i 、Removal rate of nitrite Z i , and the conversion rate of nitrogen in N2O4 after neutralization Y i , wherein the nitrite comprises nitrous acid; S5. According to the data in step S4, the optimal dosage of H2O2 is determined as: 20% excess over the theoretical dosage.

2. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 1, characterized in that: The configuration process of the nitro-oxidant wastewater solution in step S1 is as follows: S11, keep the blown ampoule ball in a constant temperature balance room for 30 minutes, weigh its mass, and record it as m0; S12. Fill each ampoule ball with 1g of liquid nitrogen tetroxide by syringe sampling method, immediately seal the tube mouth, put it into the balance room and keep it at a constant temperature for 30 minutes, weigh the mass of the ampoule ball filled with the sample, record it as m i ; S13. Gently slide the ampoule ball from the mouth of the 250mL stoppered conical bottle to the bottom of the bottle. The amount of water in the conical bottle is determined according to the mass of the N2O4 sample in the ampoule ball, so that every 100mL of distilled water contains 1g of N2O4 sample. The volume of water added is recorded as U i ; S14. When using, break the ampoule ball to dissolve the N2O4 in it into the distilled water in the conical flask.

3. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 1, characterized in that: The method also includes establishing a nitrate nitrogen standard working curve y1 and a nitrite nitrogen standard working curve y2. The nitrate nitrogen standard working curve y1 is specifically: y1=0.25442x1, and the correlation coefficient is R 2 =0.99997; the standard working curve y2 of nitrite nitrogen is specifically: y2=0.05012x2, and the correlation coefficient is R 2 =0.99951.

4. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 2, characterized in that: The concentration of nitrate nitrogen in wastewater before neutralization c Ai The determination process is as follows: after adding H2O2 in step S2, the wastewater is left to stand for a certain period of time, and after the nitrite and nitrite ions in the wastewater fully react with H2O2, the supernatant volume V is immediately removed with a pipette. A , nitrate nitrogen concentration was determined by spectrophotometry.

5. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 4, characterized in that: The neutralization is to add 2 drops of phenolphthalein indicator solution, the unit is 10g / L, and titrate with a calibrated NaOH solution until the solution turns pink and keeps it without fading for 30s. At the same time, a control test is performed, and the actual concentration of the calibrated sodium hydroxide solution is recorded as Its unit is mol / L, and the volume of NaOH solution consumed is recorded as V i , the volume of NaOH solution consumed in the control experiment is recorded as V1.

6. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 1, characterized in that: Ionization degree of nitrite in wastewater before neutralization β i The calculation formula is:

7. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 1, characterized in that: Removal rate of nitrite in wastewater before neutralization Z i The calculation formula is: Among them, nitrite contains nitrous acid.

8. The method for verifying the dosage of hydrogen peroxide for treating nitro-oxidant wastewater according to claim 1, characterized in that: The conversion rate of nitrogen in N2O4 after neutralization is Y i The calculation formula is:

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