Application of filter electrode in reduction and recovery of complex copper in wastewater

Abstract

The invention relates to application of a filter electrode in reduction and recovery of complex copper in wastewater, and relates to the technical field of water treatment. According to the application of the filter type electrode to recovery of the metal copper from the wastewater containing the organic complex copper, the filter type electrode takes a carbon felt as a substrate, and the surface of the substrate is coated with an active layer containing polybenzimidazole; the active layer further comprises a binder and a conductive agent; when the filter type electrode filters the feeding liquid containing the complex copper, the electroreduction reaction is carried out, copper is deposited on the surface of the electrode in a metal simple substance mode, and recovery of copper resources in the wastewater containing the organic complex copper is achieved. The filter electrode has the advantages of low energy consumption, high stability and the like, copper ions in wastewater can be directly captured without complex breaking, and efficient electroreduction of organic complex copper is realized.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to the application of a filter electrode in the reduction and recovery of complexed copper in wastewater. Specifically, it relates to a method for preparing and applying a filter cathode that can directly recover complexed copper from wastewater without the need for oxidation and complex breaking, and is suitable for the recovery of heavy metal copper from industrial wastewater containing organic complexed copper. Background Technology

[0002] According to statistics from the United Nations Environment Programme (UNEP), the total amount of copper-containing industrial wastewater discharged globally each year exceeds 2 million tons. Heavy metals are highly biotoxic and can accumulate through the food chain. If not properly treated and discharged into natural water bodies, they will seriously threaten regional water environments and the safety of drinking water for residents. Copper-containing wastewater possesses both pollution and resource attributes, and the economic potential for copper resource enrichment and recovery from wastewater is enormous (the value of copper recovery exceeds 60,000 RMB / ton). Copper in industrial wastewater often forms stable complexes (HMCs) with organic ligands (EDTA, citric acid, etc.), accounting for as much as 60-80%.

[0003] Existing technologies often limit the efficiency of complexed copper recovery due to low complex-breaking efficiency (<30%). For example, non-redox separation methods (adsorption, membrane separation) are affected by coexisting ions and cannot dissociate complex bonds; oxidative decomposition-recovery methods (Fenton reaction, ozone oxidation) suffer from high oxidant consumption, secondary pollution from mineralized ligands, and high energy consumption (0.5~1.5 kWh / g). Therefore, there is an urgent need to develop efficient recovery technologies to achieve the dual goals of pollution control and resource regeneration. Electrochemical reduction technology has become one of the emerging technologies for the recovery of complexed heavy metals in recent years due to its advantages such as simultaneous complex-breaking recovery and no secondary pollution. However, electroreduction technology is limited by the blocking and orbital occupation of electron transfer pathways at the center of heavy metals by ligands, requiring the continuous application of high cathode potentials to overcome the limitations of the electron transfer reduction process, and still faces the key problem of bottleneck in complex-breaking recovery efficiency. Summary of the Invention

[0004] To address the above technical problems, this invention provides an application of a filter electrode in the reduction and recovery of complexed copper in wastewater. By constructing a functionalized ligand with strong coordination activity at the electrode interface, the lone pair electrons of the ligand specifically coordinate with the empty orbitals of the target heavy metal ions, competitively replacing the weakly bound ligands in the original complex. This achieves spontaneous breakdown of the complexed heavy metal and establishes a direct and efficient electron transfer channel between the heavy metal ions and the electrode surface, thereby reducing the activation energy barrier and overpotential required for the heavy metal ion reduction reaction. Simultaneously, the heavy metal element generated by in-situ electroreduction on the cathode surface can catalyze the generation of active hydrogen atoms (H atoms) from water molecules (or protons). *The combined effects of -2.3 V vs. SHE promote the reduction of complexed heavy metals. In addition, to address the key issues of insufficient mass transfer rate and low utilization of active sites at the interface of the flow-through electrode in traditional electrochemical systems, a filtration-type electroreduction system is constructed. By enhancing the interfacial convection mass transfer effect, the mass transfer efficiency is improved. A coupled system of autocatalytic electroreduction and flow-through enhanced mass transfer is established, breaking through the bottleneck of traditional electroreduction technology and significantly improving the removal efficiency of complexed heavy metals and the energy efficiency of resource recovery.

[0005] The purpose of this invention is to provide an application of a filter electrode in the reduction and recovery of complexed copper in wastewater. The filter electrode uses carbon felt as a substrate and has an active layer containing polybenzimidazole wrapped on the surface of the substrate. The active layer also includes an adhesive and a conductive agent; When filtering feed liquid containing complexed copper, the filter electrode performs an electroreduction reaction, and copper is deposited on the electrode surface in the form of elemental metal, thus realizing the recovery of copper resources in wastewater containing organic complexed copper.

[0006] In some embodiments of the present invention, the filter electrode is prepared by the following method: Conductive ink is obtained by mixing polybenzimidazole, binder and conductive agent in a solvent and then ultrasonically mixing. The obtained conductive ink is drop-coated onto the substrate surface and dried to obtain a filter electrode.

[0007] In some embodiments of the present invention, the polybenzimidazole has a molecular weight of 50,000 to 100,000 and a purity of 95% to 100%.

[0008] In some embodiments of the present invention, the binder comprises PVDF and / or perfluorosulfonic acid resin; the conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene; The solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0009] In some embodiments of the present invention, the mass ratio of the polybenzimidazole, conductive agent and binder is (6~8):(1~3):1.

[0010] In some embodiments of the present invention, the concentration of polybenzimidazole in the conductive ink is 0.0625 wt% to 0.25 wt%.

[0011] In some embodiments of the present invention, the ultrasound duration is 10-30 min and the reaction temperature is 25-30°C.

[0012] In some embodiments of the present invention, the concentration of complexed copper in the wastewater is 4.5~32 mg / L.

[0013] In some embodiments of the present invention, the complexed copper in the wastewater includes one or more of Cu-EDTA, Cu-HEDTA, Cu-EDDA, ​​Cu-IDA, Cu-NTA, Cu-Gly, and Cu-citric acid.

[0014] The same principles apply to the explanation of the mechanisms in other common complexed copper systems (such as Cu-HEDTA, Cu-EDDA, ​​Cu-IDA, Cu-NTA, Cu-Gly, and Cu-citric acid). 1. The universality of competitive coordination: imidazole groups on Cu 2+ It possesses moderately strong coordination ability (stability constant logβ4 is approximately 12.6). Although different complexing agents have varying effects on Cu... 2+ The stability constants vary, but the high local concentration and surface confinement effect of imidazole groups on the electrode surface enable them to effectively compete for Cu in various complexing agents. 2+ This includes systems with stability constants similar to or even slightly higher than EDTA. Coordination chemistry principles indicate that capture can be achieved as long as the coordination ability of the imidazole group is sufficient to disrupt the original complexation equilibrium, which is essentially no different from the EDTA system.

[0015] 2. Reconstruction of electron transfer channels is a universal mechanism: regardless of the original complexing agent, the imidazole group captures Cu. 2+ Subsequently, an "imidazole-Cu" intermediate is formed on the electrode surface. This intermediate has a more favorable electron transfer pathway, allowing Cu... 2+ This allows the shielding effect of the original complexing agent to be bypassed, directly gaining electrons to be reduced to elemental copper. This mechanism is independent of the type of the original complexing agent, depending only on the interaction between the imidazole group and Cu. 2+ Specific interactions between them.

[0016] In summary, this invention focuses on "imidazolium group competitive coordination + electron transfer channel reconstruction," and is not specifically targeting EDTA as a complexing agent, but rather all copper complexes that can be competitively coordinated by imidazolium groups. Those skilled in the art can reasonably foresee that the method can be extended to common complexed copper wastewater systems.

[0017] In some embodiments of the present invention, the water flux filtered during the filter electrode filtration process is 150~2400 L / (m²). 2 ∙h), for example, can be 450, 600, 1200, 2400 L / (m 2 ∙h) etc., the working voltage of the electroreduction reaction is 1.5~2.5 V.

[0018] The core technical approach of this invention is: modifying the surface of a carbon felt with polybenzimidazole (OPBI) to construct a filter-type active electrode, utilizing the imidazole group to form a complex with the target copper (such as Cu-EDTA) in the Cu.2+ The competitive coordination of the copper ions "steals" copper ions from the original complexing agent and reconstructs the "polybenzimidazole-Cu" electron transfer channel on the electrode surface, thereby achieving efficient electroreduction deposition of copper on the electrode surface.

[0019] The technical solution of the present invention has the following advantages compared with the prior art: By constructing functionalized ligands with strong coordination activity at the electrode interface, the lone pair electrons of the pyridine nitrogen on the imidazole ring of polybenzimidazole specifically coordinate with the empty orbitals of the target heavy metal ions, competitively replacing the weakly bound ligands in the original complex. This achieves spontaneous breakdown of the complexed heavy metal and establishes a direct and efficient electron transfer channel between the heavy metal ions and the electrode surface, reducing the activation energy barrier and overpotential required for the heavy metal ion reduction reaction. Simultaneously, the in-situ formation of the Cu-N4 catalytic structure on the cathode surface and the heavy metal element generated by in-situ electroreduction co-catalyze the formation of active hydrogen atoms from water molecules (or protons), jointly promoting the reduction of the complexed heavy metal. Furthermore, addressing the key issues of insufficient mass transfer rate and low utilization of active sites in traditional electrochemical systems due to the flow-through electrode interface, a filtration-type electroreduction system is constructed. By enhancing interfacial convection mass transfer, the mass transfer efficiency is improved, establishing a coupled system of autocatalytic electroreduction and flow-through enhanced mass transfer. This breaks through the bottleneck of traditional electroreduction technology, significantly improving the removal efficiency and resource recovery efficiency of the complexed heavy metal copper. Meanwhile, the filter electrode involved in this invention has good mechanical strength and stability, and can be used for the stable recovery of heavy metal copper from industrial wastewater containing organic complexed copper. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 Microscopic morphology diagrams of the carbon felt substrate used in this invention and the filter electrode prepared by the preparation method provided in Example 1.

[0021] Figure 2 The efficiency of electroreduction recovery of Cu-EDTA using the filter electrode obtained in Example 1 under the operating conditions provided in Example 2.

[0022] Figure 3 The efficiency of electroreduction recovery of Cu-EDTA using the filter electrode obtained in Example 1 under the operating conditions provided in Example 3.

[0023] Figure 4 The efficiency of electroreduction recovery of Cu-EDTA using the filter electrode obtained in Example 1 under the operating conditions provided in Example 4.

[0024] Figure 5This demonstrates the efficiency of electroreduction recovery of organically complexed copper from actual industrial wastewater using the filter electrode obtained in Example 1 under the operating conditions provided in Example 5.

[0025] Figure 6 To assess the efficiency of electroreduction recovery of Cu-EDTA and Ni-EDTA using the filter electrode obtained in Example 1 under the operating conditions provided in Example 6. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing a filter electrode for copper resource recovery from wastewater containing organically complexed copper, which is carried out according to the following steps: Step S1 Preparation of polybenzimidazole conductive ink: 0.2 g of polybenzimidazole powder with a purity of 99.9% (polybenzimidazole molecular weight of 100,000, purity of 95%~100%), 0.025 g of PVDF powder with a purity of 95% and 0.025 g of conductive carbon black were added to 80 mL of N-methylpyrrolidone solvent with a purity of 99.5% and ultrasonically mixed for 10 min at room temperature to obtain polybenzimidazole conductive ink.

[0029] Step S2: Preparation of polybenzimidazole-modified carbon felt filter electrode: A 20 × 20 × 2 mm carbon felt substrate was immersed in the polybenzimidazole conductive ink prepared in S1, ultrasonically treated for 30 min, and then removed. The treated carbon felt was then dried in a forced-air dryer at 80℃ for 12 h to obtain the polybenzimidazole-modified carbon felt, which is the filter electrode used for copper resource recovery from complexed copper wastewater. The obtained polybenzimidazole-modified carbon felt and the unmodified carbon felt substrate were structurally characterized, and the results are shown in […]. Figure 1 As shown in the figure, compared with the carbon felt substrate, the carbon fiber surface of the filter electrode obtained in this embodiment of the invention is uniformly coated with a layer of polybenzimidazole.

[0030] Example 2

[0031] The quartz crystal microbalance was tested using polybenzimidazole as described in Example 1. The specific steps are as follows: Step S1: Dissolve 500 μg of polybenzimidazole in N-methylpyrrolidone at 80℃ to obtain a loading solution; use a microsyringe to take a total of 20 μL of the loading solution in four portions and uniformly drop it onto the gold chip, with a material loading of 1 μg on each gold chip; place the gold chip in an 80℃ drying oven to dry.

[0032] Step S2: The gold chip loaded with polybenzimidazole prepared in Step S1 was used for testing with a quartz crystal microbalance. For the first 1000 s after the start of the experiment, 5 mmol / L Na₂SO₄ solution was used as the feed solution; after 1000 s, 5 mmol / L Na₂SO₄ + 0.5 mmol / L Cu-EDTA was used as the feed solution. No electricity was applied before 1200 s, and after 2500 s, a constant cathode potential of -0.6 V was applied to the gold chip via an electrochemical workstation.

[0033] Using an unmodified gold chip as a control, the specific strong coordination capture and in-situ electroreduction of Cu-EDTA by polybenzimidazole are as follows: Figure 2 As shown in the figure, if only adsorption occurs, the curve tends to flatten when adsorption saturation is reached; if an electrochemical reduction reaction occurs, the elemental metal will be deposited on the gold chip, and the mass of the gold chip will continuously increase. Without an applied electrode, the adsorption of Na2SO4 on the polybenzimidazole-modified gold chip is almost negligible. With the addition of Cu-EDTA, the mass of the gold chip slowly increases due to the coordination capture of the complexed heavy metal by PBI. After applying a constant cathode potential, the mass increases significantly due to the deposition of elemental copper on the gold chip. These experimental results confirm that polybenzimidazole exhibits a specific strong coordination capture-in-situ electroreduction process when electrorecovering heavy metals from Cu-EDTA.

[0034] Example 3

[0035] The filter electrode prepared in Example 1 was used as the cathode, and the carbon felt as the anode, with a distance of 1 mm between the cathode and anode. The experimental water sample was laboratory-prepared Cu-EDTA wastewater containing 50 mmol / L Na₂SO₄ for conductivity. The initial Cu-EDTA concentration was 32 mg Cu / L, and the flux was 450 L / (m²). 2 Filtration was performed under the condition of ·h), with water flowing from the cathode to the anode. When the cell voltage was 1.5V, 2.0V, 2.5V, and 3.0V, the recovery rates of copper resources in the water were 43%, 84%, 93%, and 96%, respectively, and remained stable within 2 hours. The experimental results are shown in [Figure number missing]. Figure 3 .

[0036] Example 4

[0037] The filter electrode prepared in Example 1 was used as the cathode, and carbon felt as the anode, with a distance of 1 mm between the cathode and anode. The experimental water sample was laboratory-prepared Cu-EDTA wastewater containing 50 mmol / L Na₂SO₄ for conductivity. The initial Cu-EDTA concentration was 32 mg Cu / L. Filtration was performed at a cell pressure of 2.5 V, with the water flow direction from the cathode to the anode. The flux was 450 L / (m²). 2 ·h), 600 L / (m 2 ·h), 1200 L / (m 2 ·h), 2400 L / (m 2 At 2 hours, the recovery rates of copper resources in water were 93%, 89%, 71%, and 53%, respectively, and remained stable within 2 hours. The experimental results are shown in [Figure number missing]. Figure 4 .

[0038] Example 5

[0039] Using the filter electrode prepared in Example 1 as the cathode and the carbon felt as the anode, with a cathode-anode spacing of 1 mm, at a flux of 150 L / (m²) 2 Filtration was performed under the condition of ·h), with the water flow direction from the cathode to the anode. The experimental water sample was copper-containing industrial wastewater from an integrated circuit company. The initial concentration of organically complexed copper was 4.5 mg Cu / L. When the cell pressure was 2.5 V, the recovery rate of copper resources in the water could reach up to 100%, and remained stable within 4 hours. The copper concentration in the effluent was far lower than the 0.5 mg / L specified in the national standard GB 39731-2020. The experimental results are shown in […]. Figure 5 .

[0040] Example 6

[0041] The filter electrode prepared in Example 1 was used as the cathode, and the carbon felt as the anode, with a distance of 1 mm between the cathode and anode. The experimental water samples were laboratory-prepared Cu-EDTA and Ni-EDTA wastewater. Both wastewaters had an initial complexed heavy metal concentration of 0.5 mmol / L and contained 50 mmol / L Na₂SO₄ for conductivity. The flux was 450 L / (m²). 2 Under the conditions of (∙h), with water flowing from the cathode to the anode, and a cell voltage of 2.5 V, the recovery rate of copper resources in the water was 93%, while the recovery rate of nickel resources was only 5%. Under these experimental conditions, the filter electrode exhibits specificity for copper resource recovery. The experimental results are shown in [Figure number missing]. Figure 6 .

[0042] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An application of a filter electrode in the reduction and recovery of complexed copper in wastewater, characterized in that, The filter electrode uses carbon felt as a substrate, and an active layer containing polybenzimidazole is wrapped on the surface of the substrate. The active layer also includes an adhesive and a conductive agent; When filtering feed liquid containing complexed copper, the filter electrode performs an electroreduction reaction, and copper is deposited on the electrode surface in the form of elemental metal, thus realizing the recovery of copper resources in wastewater containing organic complexed copper.

2. The application according to claim 1, characterized in that, The filter electrode is prepared by the following method: Conductive ink is obtained by mixing polybenzimidazole, binder and conductive agent in a solvent and then ultrasonically mixing. The obtained conductive ink is drop-coated onto the substrate surface and dried to obtain a filter electrode.

3. The application according to claim 2, characterized in that, The polybenzimidazole has a molecular weight of 50,000 to 100,000 and a purity of 95% to 100%.

4. The application according to claim 2, characterized in that, The adhesive includes PVDF and / or perfluorosulfonic acid resin; The conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and graphene. The solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

5. The application according to claim 2, characterized in that, The mass ratio of the polybenzimidazole, conductive agent and binder is (6~8):(1~3):

1.

6. The application according to claim 2, characterized in that, The concentration of polybenzimidazole in the conductive ink is 0.0625 wt% to 0.25 wt%.

7. The application according to claim 2, characterized in that, The ultrasound duration is 10-30 minutes, and the reaction temperature is 25-30°C.

8. The application according to claim 1, characterized in that, The concentration of complexed copper in the wastewater was 4.5~32 mg / L.

9. The application according to claim 1, characterized in that, The complexed copper in the wastewater includes one or more of Cu-EDTA, Cu-HEDTA, Cu-EDDA, ​​Cu-IDA, Cu-NTA, Cu-Gly, and Cu-citric acid.

10. The application according to claim 1, characterized in that, The water flux filtered during the filter electrode filtration process is 150~2400 L / (m²). 2 The working voltage for the electroreduction reaction is 1.5~2.5 V.

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