Method for treating waste water containing formaldehyde and sodium nitrite by copper elemental catalyst

Abstract

A method for treating wastewater containing formaldehyde and sodium nitrite by copper elemental catalysis, which relates to the field of waste water treatment and metal catalysis. Method: adjust the pH value of wastewater containing formaldehyde and sodium nitrite to alkaline, then add copper element, and react under stirring condition, so that the interface conversion of formaldehyde on the surface of copper element occurs, and the removal of sodium nitrite is promoted, thereby realizing the synchronous treatment of formaldehyde and sodium nitrite. The electron paramagnetic resonance results show that the characteristic signal related to hydrogen free radical capture can be detected in the copper powder / formaldehyde system. The experimental results show that when the dosage of copper powder is 1 g / L, the removal rates of formaldehyde and nitrite are obviously improved. The application utilizes the transformation of formaldehyde from "pollutant to be removed" to "convertible reaction substrate", realizes the removal of nitrite without additional addition of traditional reducing agent, and provides a new method for the collaborative treatment of wastewater containing formaldehyde and sodium nitrite.

Description

Technical Field

[0001] This invention relates to the fields of wastewater treatment and metal catalysis, specifically to a method for treating wastewater containing formaldehyde and sodium nitrite using copper elemental catalysis. Background Technology

[0002] Formaldehyde is a typical industrial organic pollutant that can originate from chemical copper plating, resin processing, adhesive production, electronic industry cleaning, and other production processes that use formaldehyde or formaldehyde-releasing additives. Sodium nitrite exists primarily in the form of nitrite ions in water bodies and is one of the important pollutants in nitrogen-containing wastewater, originating from chemical, surface treatment, and electronics industries, as well as related nitrogen-containing wastewater treatment processes. These pollutants coexist or require joint treatment in some industrial wastewater or mixed wastewater treatment units. If they cannot be effectively removed, they will not only increase the load on subsequent treatment processes but may also adversely affect the aquatic environment and biological treatment systems.

[0003] Current treatment approaches typically treat formaldehyde and nitrite as two separate pollutants for removal. For formaldehyde, common methods include oxidation, biochemical processes, adsorption, and catalytic conversion; for nitrite, common methods include biological denitrification, chemical reduction, ion exchange, and adsorption. While these methods have a certain level of application, they still have shortcomings when treating combined wastewater containing formaldehyde and nitrite: formaldehyde has strong reactivity and some biotoxicity, which may affect the effectiveness of subsequent biological treatment; the nitrite reduction process usually requires suitable electron donors, microbial conditions, or external reducing agents; and treating the two pollutants separately often increases process length, reagent consumption, and operating costs. Therefore, developing a treatment method that couples the formaldehyde conversion process with the nitrite removal process is of practical significance.

[0004] Compared to catalytic materials that require complex preparation processes, elemental copper materials are simple in composition, readily available, and low in cost, making them convenient for application in wastewater treatment systems. However, research and application of elemental copper in promoting formaldehyde interfacial conversion and further for simultaneous nitrite removal remain relatively limited in the current technology. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for treating wastewater containing formaldehyde and sodium nitrite using copper elemental catalysis.

[0006] This invention promotes the interfacial transformation of formaldehyde in strongly alkaline water through a copper elemental catalyst, and further promotes the removal of nitrite, thereby achieving the simultaneous treatment of formaldehyde and sodium nitrite.

[0007] A method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis is specifically carried out according to the following steps:

[0008] The pH of the wastewater containing formaldehyde and sodium nitrite is adjusted to alkaline, and then elemental copper is added. The reaction is carried out under stirring conditions, which causes the formaldehyde to undergo interfacial transformation on the surface of elemental copper and promotes the removal of sodium nitrite, thereby achieving the simultaneous treatment of formaldehyde and sodium nitrite.

[0009] The principle of this invention:

[0010] Formaldehyde can undergo the Cannizzaro reaction and related transformations under strongly alkaline conditions, converting it into formate, methanol, and other products. Introducing a metal material with surface catalytic capabilities into the system allows for further transformation of formaldehyde at the metal / solution interface, forming reducing hydrogen radicals. Copper is widely available, inexpensive, and possesses certain surface catalytic capabilities; its introduction into strongly alkaline formaldehyde systems is expected to promote interfacial transformation of formaldehyde and link the formaldehyde transformation process with nitrite removal.

[0011] In the copper-catalyzed formaldehyde conversion system, formaldehyde can undergo interfacial transformation on the copper powder surface, forming hydrogen free radicals. Nitrite is a highly water-soluble inorganic pollutant, mainly distributed in the bulk solution. The reducing active species generated in the copper powder / formaldehyde system may not be entirely confined to the copper powder surface; some of them can enter the bulk solution and participate in NO2 conversion. - The tendency to remove formaldehyde; therefore, using copper powder to promote the interfacial transformation of formaldehyde and coupling this process with the removal of nitrite can provide a new synergistic treatment approach for wastewater containing formaldehyde and sodium nitrite.

[0012] This invention transforms formaldehyde from a "pollutant to be removed" into a substrate that can participate in the reaction. Copper powder with an average particle size of about 80 nm is used as an interfacial catalyst to promote the conversion of formaldehyde and simultaneously reduce the concentration of nitrite under strongly alkaline conditions. This method differs from treating nitrite by adding an external reducing agent alone, and also from simply removing formaldehyde. Instead, it couples the formaldehyde removal and nitrite removal processes, providing a synergistic treatment method for wastewater containing formaldehyde and sodium nitrite.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] I. This invention utilizes formaldehyde as a convertible substrate in the reaction system, transforming formaldehyde from a single pollutant to be removed into a reaction substrate that participates in nitrite removal, thereby achieving the coupling of formaldehyde removal and nitrite removal.

[0015] Second, this invention uses copper powder with an average particle size of about 80 nm as a catalyst. Copper is widely available, inexpensive, and easy to obtain, and has good material availability and application cost advantages.

[0016] Third, the electron paramagnetic resonance results in this invention show that characteristic signals related to hydrogen radical capture can be formed in the copper powder / formaldehyde system, indicating that copper powder can promote the formaldehyde interface transformation and generate hydrogen radicals with reducing ability.

[0017] IV. In this invention, nitrite is mainly distributed in the bulk solution, while the reducing hydrogen radicals generated in the copper powder / formaldehyde system may enter the bulk solution and participate in NO2. - The tendency to remove nitrites is beneficial for promoting their removal.

[0018] V. In this invention, when the amount of copper powder added is increased from 0.2 g / L to 1 g / L, the formaldehyde removal rate and nitrite removal rate are significantly improved, indicating that increasing the active sites on the copper surface is beneficial to improving the reaction performance of the system.

[0019] VI. This invention does not require the addition of traditional reducing agents other than formaldehyde removal agents, and the process is simple, providing a new method for the synergistic treatment of wastewater containing formaldehyde and sodium nitrite. Attached Figure Description

[0020] Figure 1 The BET adsorption-desorption isotherm and pore size distribution of copper powder are shown.

[0021] Figure 2 SEM image of copper powder;

[0022] Figure 3 The XRD pattern of copper powder;

[0023] Figure 4 TEM and HRTEM images of copper powder;

[0024] Figure 5 EPR diagram of hydrogen radicals in a 1 g / L copper powder / formaldehyde system;

[0025] Figure 6 The graph shows the change in formaldehyde removal rate with reaction time under different copper powder dosages.

[0026] Figure 7 The graph shows the change in sodium nitrite removal rate with reaction time under different copper powder dosages. Detailed Implementation

[0027] Specific Implementation Method 1: This implementation method is a method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis, specifically carried out according to the following steps:

[0028] The pH of the wastewater containing formaldehyde and sodium nitrite is adjusted to alkaline, and then elemental copper is added. The reaction is carried out under stirring conditions, which causes the formaldehyde to undergo interfacial transformation on the surface of elemental copper and promotes the removal of sodium nitrite, thereby achieving the simultaneous treatment of formaldehyde and sodium nitrite.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the pH value of the wastewater containing formaldehyde and sodium nitrite is adjusted to 13. All other steps are the same as in Specific Implementation Method One.

[0030] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the sodium nitrite in the formaldehyde and sodium nitrite wastewater is expressed as NO2. - NO2 - The initial concentration is 1 mmol / L. Other steps are the same as in specific implementation method one or two.

[0031] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the initial concentration of formaldehyde in the formaldehyde-containing and sodium nitrite-containing wastewater is 0.1 mol / L to 0.4 mol / L. The other steps are the same as in Specific Implementation Methods One to Three.

[0032] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the initial concentration of formaldehyde in the formaldehyde-containing and sodium nitrite-containing wastewater is 0.3 mol / L. The other steps are the same as in Specific Implementation Methods One to Four.

[0033] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the copper element is copper powder with an average particle size of 80 nm. The other steps are the same as in Specific Implementation Methods One to Five.

[0034] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the dosage of elemental copper is 0.2 g / L to 1 g / L. The other steps are the same as in Specific Implementation Methods One to Six.

[0035] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the amount of elemental copper added is 0.5 g / L. The other steps are the same as in Specific Implementation Methods One to Seven.

[0036] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the reaction time under stirring conditions is 1 to 6 hours. Other steps are the same as in Specific Implementation Methods One to Eight.

[0037] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: the reaction process is monitored by detecting the formaldehyde concentration and NO2 in the reaction solution. - The concentration change is evaluated; elemental copper can form hydrogen radicals or related reducing active species in the system, which can be detected by electron paramagnetic resonance. Other steps are the same as in specific embodiments one to nine.

[0038] The beneficial effects of the present invention are verified using the following embodiments:

[0039] Example 1: Structural characterization of copper powder, specifically completed according to the following steps:

[0040] I. The specific surface area and pore structure of copper powder with an average particle size of approximately 80 nm were tested using BET.

[0041] II. SEM was used to observe the particle morphology and agglomeration state of copper powder;

[0042] III. XRD analysis of the crystal phase composition of copper powder;

[0043] IV. TEM and HRTEM were used to observe the local morphology, lattice fringes, and crystal plane information of copper powder.

[0044] The BET, SEM, XRD, TEM, and HRTEM results of copper powder are shown in the figures below. Figures 1-4 .

[0045] Characterization results show that the BET specific surface area of ​​copper powder with an average particle size of approximately 80 nm is 5.9181 m². 2 The concentration of copper powder per gram (g) indicates that the effective contact area exposed by the copper powder is relatively limited. SEM results show that the copper powder is generally irregularly granular with some agglomeration. XRD results show that the sample has obvious diffraction peaks at 2θ of approximately 43.3°, 50.4°, and 74.1°, corresponding to the (111), (200), and (220) crystal planes of metallic Cu, respectively, indicating that the sample is mainly composed of face-centered cubic metallic copper; among them, the Cu(111) diffraction peak has a higher intensity, indicating that Cu(111) may be the main exposed or dominant orientation crystal plane. TEM and HRTEM results further show that the copper particles have a local agglomeration structure and clear lattice fringes; the interplanar spacing was measured to be approximately 0.208 nm, which is consistent with the Cu(111) crystal plane. The above results indicate that the copper powder used is mainly composed of metallic Cu phase, which can provide a metallic reaction surface for formaldehyde interfacial transformation.

[0046] Example 2: Detection of hydrogen free radicals in the copper powder / formaldehyde system, specifically performed according to the following steps:

[0047] 1. Add 9.675 mL of deionized water to the reaction vessel, and then add sodium hydroxide to make the pH of the system 13;

[0048] 2. Add 0.225 mL of formaldehyde stock solution with a concentration of 13.33 mol / L to the alkaline system obtained in step 1 to make the initial formaldehyde concentration 0.3 mol / L;

[0049] 3. Add 100 μL of 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) as a spin trapping agent to the system obtained in step 2;

[0050] IV. Add 0.010 g of copper powder with an average particle size of about 80 nm to the system obtained in step III, so that the amount of copper powder added is 1 g / L, and start the reaction.

[0051] V. Samples were taken at 5 min, 10 min and 30 min after the reaction started, and detected by electron paramagnetic resonance.

[0052] EPR results of hydrogen radicals in the copper powder / formaldehyde system are shown in the figure. Figure 5 ;

[0053] EPR results showed that in the 1 g / L copper powder / formaldehyde system, a distinct multiple characteristic peak signal was detected after 5 min of reaction; the signal remained relatively strong after 10 min; and a related signal was still detectable after 30 min. This indicates that under strongly alkaline conditions, copper powder can promote interfacial transformation of formaldehyde on its surface, generating hydrogen radicals that can be captured by DMPO. Considering the high solubility of nitrite and its predominantly bulk distribution in the solution, it can be inferred that some of the hydrogen radicals formed in the copper powder / formaldehyde system can enter the bulk solution and participate in NO2 formation. - The above results provide evidence of active species that enable copper powder to promote the removal of nitrite.

[0054] Example 3: A method for treating wastewater containing formaldehyde and sodium nitrite using copper powder catalysis is specifically carried out according to the following steps:

[0055] 1. The total volume of the reaction system is 100 mL. Add 97.75 mL of deionized water to the reaction vessel, then add 6.90 mg of sodium nitrite to reduce the NO2 content in the reaction system. - The initial concentration was 1 mmol / L; then 2.25 mL of formaldehyde stock solution with a concentration of 13.33 mol / L was added to make the initial formaldehyde concentration 0.3 mol / L.

[0056] 2. Add sodium hydroxide to the sodium nitrite-containing water obtained in step 1 to adjust the pH of the reaction system to 13;

[0057] 3. Under stirring conditions, add 0.020 g and 0.100 g of copper powder with an average particle size of about 80 nm to the two portions of the reaction system obtained in step 2, respectively, so that the copper powder addition amounts are 0.2 g / L and 1 g / L, and mix evenly.

[0058] IV. Reaction Initiation: The reaction was carried out at room temperature with continuous stirring. Samples were taken at set intervals during the reaction. The collected reaction solution was filtered through a 0.22 μm filter membrane, and the formaldehyde concentration and NO2 concentration in the supernatant were measured. - The concentration was determined, and the formaldehyde removal rate and nitrite removal rate were calculated.

[0059] A blank control group was set up, without adding copper powder, and the other steps and parameters were the same as above, to compare the removal of formaldehyde under copper-free conditions.

[0060] The formaldehyde removal rate results under different copper powder dosages are shown in the figure. Figure 6 ;

[0061] Experimental results show that copper powder can significantly promote formaldehyde removal and simultaneously promote nitrite removal. Regarding formaldehyde removal, in the blank group, formaldehyde only underwent limited alkaline self-reaction, with a removal rate of approximately 23% after 6 hours. When the copper powder dosage was 0.2 g / L, the formaldehyde removal rate gradually increased with reaction time, approaching 100% after 6 hours. When the copper powder dosage was 1 g / L, the formaldehyde removal rate further accelerated, reaching approximately 95% after 1 hour, and almost completely removed after 2 hours. These results indicate that copper powder can significantly accelerate the formaldehyde conversion process, and higher dosages are more conducive to rapid formaldehyde removal.

[0062] The results of sodium nitrite removal rates under different copper powder dosages are shown in the figure. Figure 7 ;

[0063] Regarding nitrite removal, when the copper powder dosage is 0.2 g / L, NO2... - The removal rate gradually increased with reaction time, reaching approximately 30% after 6 hours; when the copper powder dosage was 1 g / L, NO2... - The removal rate was significantly improved, reaching approximately 51% after 1 hour, 78% after 2 hours, and stabilizing at approximately 92% after 3 hours. This indicates that increasing the copper powder dosage significantly enhanced the removal of nitrite from the system.

[0064] The above results indicate that copper powder not only promotes the interfacial transformation of formaldehyde in a strongly alkaline system, but also couples this transformation process with nitrite removal. Combined with the EPR results in Example 2, it can be seen that the hydrogen radicals or related reducing active species formed in the copper powder / formaldehyde system may be important factors promoting nitrite removal. Since nitrite is a highly water-soluble inorganic pollutant, mainly distributed in the bulk solution, while NO2 in the 1 g / L copper powder system... - The rapid increase in removal rate in the early stage of the reaction indicates that the hydrogen free radicals generated on the copper powder surface may not be completely confined to the copper powder surface; some of them can enter the bulk solution and react with NO2. -The reaction occurs. As the copper powder dosage increases from 0.2 g / L to 1 g / L, the number of available copper surface active sites in the system increases, the formaldehyde conversion is faster, and the generation of hydrogen free radicals that can enter the bulk phase and participate in the reaction is more complete, thus exhibiting a higher formaldehyde removal rate and nitrite removal rate.

Claims

1. A method for treating wastewater containing formaldehyde and sodium nitrite using copper elemental catalysis, characterized in that... The method is specifically implemented according to the following steps: The pH of the wastewater containing formaldehyde and sodium nitrite is adjusted to alkaline, and then elemental copper is added. The reaction is carried out under stirring conditions, which causes the formaldehyde to undergo interfacial transformation on the surface of elemental copper and promotes the removal of sodium nitrite, thereby achieving the simultaneous treatment of formaldehyde and sodium nitrite.

2. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... Adjust the pH of the wastewater containing formaldehyde and sodium nitrite to 13.

3. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The formaldehyde and sodium nitrite-containing wastewater contains sodium nitrite as NO2. - NO2 - The initial concentration was 1 mmol / L.

4. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The initial concentration of formaldehyde in the formaldehyde-containing and sodium nitrite-containing wastewater is 0.1 mol / L to 0.4 mol / L.

5. The method for treating formaldehyde and sodium nitrite-containing wastewater by copper catalysis according to claim 4, characterized in that... The initial concentration of formaldehyde in the wastewater containing formaldehyde and sodium nitrite was 0.3 mol / L.

6. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The copper element is copper powder with an average particle size of 80 nm.

7. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The dosage of elemental copper is 0.2 g / L to 1 g / L.

8. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 7, characterized in that... The amount of elemental copper added is 0.5 g / L.

9. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The reaction time under stirring conditions is 1 to 6 hours.

10. The method for treating wastewater containing formaldehyde and sodium nitrite using copper catalysis according to claim 1, characterized in that... The reaction process involves detecting the formaldehyde concentration and NO2 in the reaction solution. - The concentration change was evaluated; elemental copper can form hydrogen radicals or related reducing active species in the system, which can be detected by electron paramagnetic resonance.

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