Treatment method of nitrate-containing waste liquid

Abstract

The invention discloses a nitrate-containing waste liquid treatment method, which comprises: (1) waste acid treatment: diluting waste acid in a neutralization reaction kettle, adding ammonia water while stirring, controlling the temperature to be 70-95 DEG C, continuously adding ammonia water to adjust the pH value of the solution to be 7.5-10.0 after the neutralization is completed, and carrying out stirring distillation to obtain an ammonium sulfate nitrate aqueous solution or an ammonium sulfate nitrate crystal; (2) wastewater treatment: 1) wastewater steam stripping: transferring nitrate wastewater into a steam stripping kettle, adding a pH regulator to regulate the pH value to be 10-13, heating the steam stripping kettle to a boiling state by using steam, distilling, condensing and recovering nitrate in the wastewater; and 2) oxidation treatment: after steam stripping is finished, hydrogen peroxide is added into the steam stripping kettle in a boiling state, stirring reaction is performed, and the reacted wastewater can be discharged after reaching the standard. Compared with a traditional Fenton method and an activated carbon adsorption method, the method has the advantages that secondary pollutants Fe (OH) 3 generated by treatment and saturated activated carbon after adsorption can be avoided, harsh reaction conditions such as light, electricity and microwaves can be avoided, the operation cost is reduced, the method is safe, environment-friendly and free of secondary pollution, the nitrate removal rate can reach 100%, and the method is suitable for industrial production. The COD (Chemical Oxygen Demand) of the treated wastewater is less than 100mg / L, and the wastewater can reach the direct discharge standard.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for treating nitrate ester-containing waste liquid, which is particularly suitable for the treatment of industrial waste liquid containing nitrate ester waste acid and wastewater, and can realize the resource utilization of waste acid and the standard discharge of wastewater. Background Technology

[0002] The production of nitrate ester compounds (such as 1,2-propanediol dinitrate, nitroglycerin, and n-propyl nitrate) generates large quantities of waste acid and wastewater containing a certain amount of nitrate esters. These waste liquids are highly corrosive and toxic; direct discharge will severely pollute water bodies, soil, and other ecological environments, while also wasting resources. Improper treatment may lead to combustion and explosion due to the accumulation of nitrate esters. Therefore, it is essential to treat waste liquids containing nitrate ester compounds.

[0003] Currently, the mixed acids (sulfuric acid and nitric acid) generated during nitrate ester production are mostly neutralized with alkaline substances such as lime, sodium carbonate, and sodium hydroxide. Although this reduces acidity, the resulting mixture of sulfates and nitrates is difficult to recover and easily generates secondary solid waste. Regarding the treatment of nitrate ester-containing wastewater, Wang Yabing et al., in their study "Research on Treatment of Nitrate Ester Wastewater Using Stripping-Oxidation Method," used stripping of high-nitrate ester-containing wastewater at pH 8-10, followed by treatment with different mass ratios of H2O2 / FeSO4•7H2O at pH 4-12, achieving a nitrate ester removal rate of 100%. This method requires multiple pH adjustments during treatment and may also generate coagulation and precipitation, causing secondary pollution. Wu Wenli et al., in patent CN111056712A, reported a method for removing nitrate esters from nitro-nitrate ester-containing wastewater by pretreatment followed by passage through a biochemical system and an MBR membrane bioreactor, and finally activated carbon adsorption.

[0004] While this method can theoretically remove nitrates, its practical application is cumbersome and requires significant investment of manpower, resources, and time. Activated carbon is difficult to regenerate after adsorption saturation, making treatment challenging and resulting in high operating costs. These factors severely limit the large-scale application of this method. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a method for treating nitrate-containing wastewater. This method is low-cost, safe, environmentally friendly, produces no secondary pollution, and can remove up to 100% of the nitrates.

[0006] The present invention adopts the following technical solution: A method for treating nitrate-containing wastewater includes the following steps: (1) Waste acid treatment: Dilute the waste acid in a neutralization reactor, add ammonia water while stirring, control the temperature at 70-95℃, continue to add ammonia water after neutralization to adjust the pH of the solution to 7.5-10.0, and stir and distill to obtain ammonium nitrate aqueous solution or ammonium nitrate crystals; (2) Wastewater treatment: 1) Wastewater stripping: The nitrate ester wastewater is transferred into a stripping kettle, a pH adjuster is added to adjust the pH to 10-13, the stripping kettle is heated to boiling with steam, and the nitrate ester in the wastewater is recovered by distillation and condensation. 2) Oxidation treatment: After stripping, hydrogen peroxide is added to the stripping kettle while it is boiling, and the mixture is stirred to react. The wastewater after the reaction can meet the discharge standards.

[0007] Preferably, in step (1), the mass fraction of ammonia water is 25-28%. The distillation time is preferably 0.5-4 hours, and the distilled water is reused for diluting waste acid.

[0008] Preferably, in step (1), the mass fraction of nitrate ester in the waste acid is 0.1-0.5%. The optimal conditions for the complete decomposition of nitrate ester in the waste acid are: continue to add ammonia water to adjust the pH of the solution to 8.5-10, maintain a constant temperature of 85-95℃, and stir for 1-3 hours.

[0009] In step 1), the pH adjuster is selected from sodium hydroxide, potassium hydroxide, etc. The stripping temperature is 100-110℃, and the stripping time is about 2 hours. After the wastewater stripping is completed, the COD of the wastewater is about 3000 mg / L, and the mass fraction of nitrate esters is < 0.05%, which can be safely discharged, but there is still a strong pungent odor.

[0010] In step 2), the stirring reaction time is preferably 20-40 min. The molar ratio of hydrogen peroxide to nitrate ester in the stripping wastewater is preferably 3-8:1, more preferably 4-6:1. The mass fraction of hydrogen peroxide is preferably 30%. After oxidation treatment, the wastewater has no odor, and the nitrate ester removal rate is 100%, with COD < 100 mg / L, meeting the direct discharge standard.

[0011] The nitrate-containing waste liquid is waste acid and wastewater generated from the preparation of nitrate compounds. The nitrate compounds are one or more of 1,2-propanediol dinitrate, ethylene glycol dinitrate, nitroglycerin, nitrocellulose, isopropyl nitrate, n-propyl nitrate, and isosorbide dinitrate.

[0012] Compared with traditional Fenton method, activated carbon adsorption method and strong oxidant oxidation method, the method of this invention can avoid the secondary pollutants Fe(OH)3 and saturated activated carbon generated during treatment, as well as the harsh reaction conditions such as light, electricity and microwave. It also reduces operating costs and has the advantages of simple operation, safety, environmental protection, no secondary pollution, nitrate ester removal rate of up to 100%, and wastewater COD < 100 mg / L after treatment, and the wastewater can meet the direct discharge standards.

[0013] The ammonium nitrate aqueous solution obtained after neutralizing and distilling waste acid can be used as a foliar fertilizer, an emergency nitrogen supplementation and rapid adjustment fertilization method. It can be directly absorbed by the leaves to solve the problem of acute nitrogen deficiency during the crop growth period. Alternatively, it can be distilled to obtain a compound nitrogen fertilizer of ammonium nitrate, which can be used as a basic nitrogen source and a long-term fertilization solution to provide continuous nitrogen support for the entire growth period or specific stages of crops.

[0014] Under strongly alkaline conditions, H₂O₂ has the strong oxidizing power of OH⁻. - [O] then attacks the nitro group (-NO2) in the nitrate ester molecule and the organic matter from the decomposition of the nitrate ester, causing bond breaking and oxidative degradation, ultimately transforming into harmless CO2, H2O and NO3. - (or N2).

[0015] After stripping nitrate ester wastewater, this invention uses hydrogen peroxide added dropwise in a boiling state instead of 96℃ for oxidation treatment. The main advantages are as follows: (1) The synergistic effect of "alkaline hydrolysis + free radical oxidation" is more significant in boiling state: the hydrolysis rate of nitrate ester is 3-5 times faster than that in 96℃, reducing ineffective consumption (such as direct decomposition into H2O and O2), and the COD removal rate is higher under the same residence time. At the same time, it promotes the hydrolysis and oxidation of nitrate ester, which can shorten the process cycle and reduce the waste of hydrogen peroxide; (2) The stirring effect in boiling state can enhance gas-liquid mass transfer. The large number of bubbles generated make the gas and liquid phases fully mixed, and the hydrogen peroxide contacts nitrate ester and reducing substances more evenly, avoiding local high concentration leading to ineffective decomposition of hydrogen peroxide and improving the utilization rate of oxidant; (3) Boiling state does not require precise temperature control (only boiling needs to be maintained), avoiding the instability of reaction efficiency caused by temperature fluctuations in 96℃. Detailed Implementation

[0016] The following examples further illustrate the method of the present invention.

[0017] Example 1: Waste acid and washing wastewater from the preparation of 1,2-propanediol dinitrate were collected, wherein the waste acid (a mixture of sulfuric acid and nitric acid) contained 0.5% nitrate ester by mass. The specific treatment steps are as follows: (1) Waste acid treatment: Dilute 5L of pure water with 10L of waste acid in a neutralization vessel, start stirring, and slowly add 25-28% ammonia water, controlling the reaction temperature at 90℃. After neutralization, continue to add ammonia water to adjust the pH to 10.0, and stir at a constant temperature of 95℃ for 1.5h (the nitrate content was tested and found to be 0, ensuring complete decomposition). Then stir and distill for 2h, distilling off 3L of water (for the next dilution) to obtain a 45% ammonium nitrate aqueous solution, which meets the foliar fertilizer standard after testing.

[0018] (2) Wastewater treatment: 1) Wastewater stripping: Take a certain amount of washing wastewater and transfer it into a stripping kettle. Add sodium hydroxide to adjust the pH to 13. Introduce steam and heat to boiling to remove water and nitrate esters. When no oily substances flow out of the condensate, stop the stripping. At this time, the mass fraction of nitrate esters in the wastewater drops to 0.04%, the COD is 2850 mg / L, and it has a strong pungent odor.

[0019] 2) Oxidation treatment: After stripping, the wastewater has a pH of 12.5 and a temperature of 102℃. H2O2 is added at a molar ratio of 6:1 (nitrate ester to 30% H2O2). The mixture is stirred and reacted for 20 minutes. The wastewater has no irritating odor. The nitrate ester content is 0 and the COD is 66mg / L, which meets the direct discharge standard.

[0020] Example 2: Waste acid and washing wastewater from the preparation of nitroglycerin were collected, wherein the waste acid (a mixture of sulfuric acid and nitric acid) contained 0.35% nitrate ester by mass. The specific treatment steps are as follows: (1) Waste acid treatment: Dilute 6L of pure water with 12L of waste acid in a neutralization vessel, start stirring, and slowly add 25-28% ammonia water, controlling the reaction temperature at 85℃. After neutralization, continue to add ammonia water to adjust the pH to 9, and stir at a constant temperature of 90℃ for 2.5h (the nitrate content was tested and found to be 0, ensuring complete decomposition). Then stir and distill for 2.5h, distilling off 2.5L of water (for the next dilution) to obtain a 48% ammonium nitrate aqueous solution, which meets the foliar fertilizer standard.

[0021] (2) Wastewater treatment: 1) Wastewater stripping: Take a certain amount of washing wastewater and transfer it into a stripping kettle. Add sodium hydroxide to adjust the pH to 12. Introduce steam and heat to boiling to distill off water and nitrate esters. When no oily substances flow out of the condensate, stop the stripping. At this time, the mass fraction of nitrate esters in the wastewater drops to 0.03%, the COD is 2665 mg / L, and there is still a strong pungent odor.

[0022] 2) Oxidation treatment: After stripping, the wastewater has a pH of 11.4 and a temperature of 105℃. H2O2 is added at a molar ratio of 5:1 between nitrate ester and 30% H2O2. The mixture is stirred and reacted for 30 minutes. The wastewater has no irritating odor, the nitrate ester content is 0, and the COD is 76mg / L, which meets the direct discharge standard.

[0023] Example 3: Waste acid and washing wastewater from the preparation of isosorbide nitrate were collected, wherein the waste acid (a mixture of sulfuric acid and nitric acid) contained 0.1% nitrate ester by mass. The specific treatment steps are as follows: (1) Waste acid treatment: Dilute 5.5L of pure water with 11L of waste acid in a neutralization vessel, start stirring, and slowly add 25-28% ammonia water, controlling the reaction temperature at 80℃. After neutralization, continue to add ammonia water to adjust the pH to 8.5, and stir at a constant temperature of 85℃ for 2 hours (the nitrate content was tested and found to be 0, ensuring complete decomposition). Then stir and distill for 2 hours, distilling off 3.2L of water (for the next dilution) to obtain a 46% ammonium nitrate aqueous solution, which meets the foliar fertilizer standard after testing.

[0024] (2) Wastewater treatment: 1) Wastewater stripping: Take a certain amount of washing wastewater and transfer it into a stripping kettle. Add sodium hydroxide to adjust the pH to 11. Introduce steam and heat to boiling to distill off water and nitrate esters. When no oily substances flow out of the condensate, stop the stripping. At this time, the mass fraction of nitrate esters in the wastewater drops to 0.02%, the COD is 2476 mg / L, and there is a slightly irritating odor.

[0025] 2) Oxidation treatment: After stripping, the wastewater has a pH of 10.8 and a temperature of 103℃. H2O2 is added at a molar ratio of 4:1 of nitrate ester to 30% H2O2. The mixture is stirred and reacted for 40 minutes. The wastewater has no irritating odor, the nitrate ester content is 0, and the COD is 45mg / L, which meets the direct discharge standard.

[0026] Comparative Example 1 Replace step 2) of the oxidation treatment in Example 1 with: 2) Oxidation treatment: After stripping, the wastewater has a pH of 12.5 and a temperature of 96°C. Add H2O2 at a molar ratio of 6:1 for nitrate ester to 30% H2O2 and stir for 20 minutes. The remaining operations are the same as in Example 1.

[0027] The treated wastewater still had a slight pungent odor, with a nitrate content of 0.02% and a COD of 450 mg / L, which did not meet the direct discharge standards.

[0028] Comparative Example 2 Replace step 2) of the oxidation treatment in Example 2 with: 2) Oxidation treatment: After stripping, the wastewater has a pH of 11.4 and a temperature of 96°C. Add H2O2 at a molar ratio of 5:1 for nitrate ester to 30% H2O2 and stir for 30 min. The remaining operations are the same as in Example 1.

[0029] The treated wastewater still had a slight pungent odor, with a nitrate content of 0.015% and a COD of 345 mg / L, which did not meet the direct discharge standards.

[0030] The above description represents the preferred embodiments of the present invention. It should be noted that, for those skilled in the art, various modifications and refinements can be made without departing from the principles of the present invention, and these modifications and refinements should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating nitrate-containing wastewater, characterized in that, Includes the following steps: (1) Waste acid treatment: Dilute the waste acid in a neutralization reactor, add ammonia water while stirring, control the temperature at 70-95℃, continue to add ammonia water after neutralization to adjust the pH of the solution to 7.5-10.0, and stir and distill to obtain ammonium nitrate aqueous solution or ammonium nitrate crystals; (2) Wastewater treatment: 1) Wastewater stripping: The nitrate ester wastewater is transferred into a stripping kettle, a pH adjuster is added to adjust the pH to 10-13, the stripping kettle is heated to boiling with steam, and the nitrate ester in the wastewater is recovered by distillation and condensation. 2) Oxidation treatment: After stripping, hydrogen peroxide is added to the stripping kettle while it is boiling, and the mixture is stirred to react. The wastewater after the reaction can meet the discharge standards.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of ammonia is preferably 25-28%.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of nitrate ester in the waste acid is 0.1-0.5%.

4. The preparation method according to claim 1, characterized in that, In step (1), continue to add ammonia water to adjust the pH of the solution to 8.5-10, keep the temperature at 85-95℃, and stir for 1-3 hours.

5. The preparation method according to claim 1, characterized in that, In step 1), the pH adjuster is selected from sodium hydroxide and potassium hydroxide.

6. The preparation method according to claim 1, characterized in that, In step 1), the stripping temperature is 100-110℃.

7. The preparation method according to claim 1, characterized in that, In step 2), the molar ratio of hydrogen peroxide to nitrate ester in the stripping wastewater is 3-8:

1.

8. The preparation method according to claim 1, characterized in that, In step 2), the molar ratio of hydrogen peroxide to nitrate ester in the stripping wastewater is 4-6:

1.

9. The preparation method according to claim 1, characterized in that, In step 2), the nitrate ester content in the wastewater after the reaction is 0, and COD < 100 mg / L.

10. The preparation method according to claim 1, characterized in that, The nitrate-containing waste liquid is waste acid and wastewater generated from the preparation of nitrate compounds. The nitrate compounds are one or more of 1,2-propanediol dinitrate, ethylene glycol dinitrate, nitroglycerin, nitrocellulose, isopropyl nitrate, n-propyl nitrate, and isosorbide dinitrate.