Closed-loop process for realizing efficient metal recovery of electroplating wastewater and synchronous cyclic utilization of complex ligand and application of closed-loop process

Abstract

The invention relates to a closed-loop process for realizing efficient metal recovery of electroplating wastewater and synchronous cyclic utilization of a complex ligand and application. The closed-loop process comprises the following steps: adding sodium bicarbonate into the electroplating wastewater and adjusting the pH value; carrying out decomplexing reaction by taking TiO2 / FTO as a photoanode and 1T-2H MoS2 / GF as a photocathode, so that Cu (II) is reduced and deposited on the photocathode; calcining the photocathode on which the Cu (II) is deposited in a mixed atmosphere containing nitrogen and oxygen to prepare Cu (at) 1T-2H MoS2 / GF; and with Cu (at) 1T-2H MoS2 / GF as a working electrode, performing electrochemical reduction on the electrolyte which is subjected to decomplexing reaction and metal Cu recovery to obtain a high-purity EDTA solution. Compared with the prior art, the method has the advantages that bicarbonate radicals are driven by photoelectrocatalysis to generate carbonate free radicals, Cu (II)-EDTA in the electroplating wastewater is degraded, metal Cu is recovered, EDTA is regenerated and recovered in situ by utilizing an electrochemical reduction technology, a frame structure of an organic ligand is reserved while Cu is effectively separated and recovered, meanwhile, complex equipment is not needed in the treatment process, and the method is simple and convenient to operate. The operation cost is low, and engineering application is easy to realize.

Description

Technical Field

[0001] The present invention relates to the technical field of electroplating wastewater treatment, and in particular to a closed-loop process and application for realizing efficient metal recovery from electroplating wastewater and synchronous recycling of complex ligands. Background Art

[0002] In recent years, the rapid development of industries such as electroplating, mining, and chemical cleaning has led to the widespread use of organic chelating agents, including citrates, tartrates, and ethylenediaminetetraacetic acid (EDTA). When these reagents are discharged into wastewater, they easily form stable chelate complexes with coexisting heavy metal ions. Traditional chemical precipitation and adsorption processes have been proven ineffective in removing Cu(II)-EDTA complexes.

[0003] Currently, wastewater containing Cu(II)-EDTA is usually treated by coupling advanced oxidation technology with basic precipitation method. The reaction principle is to activate oxidants (such as hydrogen peroxide, peracetic acid) under catalytic conditions such as light / heat / ozone to generate highly oxidizing active free radicals (such as ·OH, SO4 - ·) to attack Cu(II)-EDTA, causing the ligand EDTA to gradually lose its complexing ability, thereby releasing free Cu 2+ , and then adjusting the pH to alkaline by adding sodium hydroxide to recover copper in the form of precipitation. Although this method has good removal effects on heavy metals and metal complexes in wastewater, there are still the following inherent limitations: 1. The process flow is relatively complex and long, increasing the difficulty of operation and management. At the same time, the investment is large, the consumption of chemicals is high, resulting in a relatively high operating cost. 2. Non-selective free radicals such as ·OH have the characteristic of non-discriminatory attack. During the complex dissociation process, they mainly oxidize the complexing agent ligand, and the complex dissociation rate is slow, hindering the release and recovery of copper ions. 3. The released free copper ions tend to re-complex with the gradually oxidized and degraded EDTA ligand to form new sub-stable complexes, resulting in an extension of the overall complex dissociation time. 4. The quality of the treated wastewater is relatively unstable, especially the concentration of copper ions may exceed the standard. Exceeding the discharge standard may require additional membrane separation technology, further increasing the treatment cost. 5. Direct oxidation of the complexing agent will cause waste of its energy, and at the same time, most of the complexing agent will eventually be converted into small molecule acids, which need further treatment before they can be discharged. Obviously, the existing treatment technology is contrary to the current advocated concept of green and sustainable development.

[0004] Chinese Patent CN202011005540.0 proposes a method for treating electroless copper plating waste liquid. First, a reducing agent is added to displace copper, then hydrogen peroxide is added for Fenton oxidation to decompose other organic substances except EDTA, and then ferric ion solution and sodium ion solution are added to synthesize sodium iron ethylenediaminetetraacetate. Through the above method, copper ions and EDTA complexing agents in the electroless copper plating waste liquid can be recovered simultaneously, and the operating cost is low. However, it still needs to add a large amount of iron powder as a reducing agent and industrial hydrogen peroxide for the Fenton reaction, and the process is complicated, requiring multiple steps of adjusting the molar ratio of ferric ions to EDTA.

[0005] Another related study proposed a Cu 0 / HCHO advanced reduction technology, which uses hydrogen free radicals to reduce Cu 2+ in the coordination complex to Cu 0 , and recovers EDTA by adjusting the pH of the system. This process provides a new idea for the resource recovery of metal wastewater, but there are still the following problems: 1. The reaction has a high pH dependence and needs to be carried out under strong alkaline conditions (pH≥13.0), resulting in an increase in treatment costs and possibly generating high-salt wastewater, increasing the subsequent neutralization or desalination burden. 2. The reaction time is too long. Laboratory adjustment requires more than 12 hours, and in large-scale applications, the treatment cycle may be extended due to insufficient reactor design or mixing efficiency, affecting the overall efficiency and economy. 3. As a toxic and harmful substance, the additional addition of formaldehyde may increase risks. Although its decomposition product formic acid (high COD) is considered environmentally friendly, excessive accumulation will increase the system complexity. 4. Although the recovered EDTA has its structure verified by FTIR, its complexing ability has not been retested, making it difficult to accurately meet the market demand for recovery.

[0006] Therefore, there is an urgent need for a process that can efficiently recover Cu metal and EDTA complex ligands in electroplating wastewater. Summary of the Invention

[0007] The purpose of the present invention is to provide a closed-loop process and application for realizing the efficient metal recovery and synchronous recycling of complex ligands in electroplating wastewater, which is easy to operate, can efficiently recover copper ions and EDTA complex ligands simultaneously, has a high copper ion recovery efficiency, and the recovered EDTA solution has excellent complexing ability.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The present invention provides a closed-loop process for realizing the efficient metal recovery from electroplating wastewater and the synchronous recycling of complex ligands, constructs a photoelectrocatalytic reaction system with TiO2 as the photoanode and 1T-2H MoS2 / GF as the photocathode, drives the generation of carbonate radicals from bicarbonate through photoelectrocatalysis to degrade Cu(II)-EDTA in electroplating wastewater, recover metallic Cu, and in-situ regenerate and recover EDTA by using an electrochemical reduction technique. The specific steps are as follows:

[0010] S1: Add sodium bicarbonate to the electroplating wastewater containing Cu(II)-EDTA and adjust the pH to obtain an electrolyte solution.

[0011] S2: Use TiO2 / FTO as the photoanode, 1T-2H MoS2 / GF as the photocathode, and a xenon lamp as the light source to perform a complex dissociation reaction on the electrolyte solution in step S1, so that Cu(II) is reduced and deposited on the photocathode to recover metallic Cu.

[0012] S3: Wash the photocathode deposited with Cu(II) obtained in step S2 and dry it under vacuum, and then calcine it in a mixed atmosphere of nitrogen and oxygen to prepare Cu@1T-2H MoS2 / GF.

[0013] S4: Construct a three-electrode system, use Cu@1T-2H MoS2 / GF obtained in step S3 as the working electrode, and perform an electrochemical reduction reaction on the electrolyte solution that has undergone the complex dissociation reaction and recovered metallic Cu in step S2.

[0014] S5: After the reduction reaction is completed, let it stand and filter to recover a high-purity EDTA solution.

[0015] Preferably, the electroplating wastewater includes wastewater generated from processes such as PCB circuit board processes and metal coating processes on the surfaces of electronic devices.

[0016] Preferably, the electroplating wastewater includes Cu(II)-EDTA.

[0017] More preferably, in addition to Cu(II)-EDTA, the electroplating wastewater also contains certain salts, metal ions, free acids, organic compounds, etc.

[0018] Preferably, in step S1, the concentration of Cu(II)-EDTA in the electrolyte solution is 0.1 mM - 1 mM, the concentration of sodium bicarbonate in the electrolyte solution is 1 - 20 mM, and the pH is adjusted to 7.5 - 8.5.

[0019] In practical applications of the present invention, the concentration of sodium bicarbonate needs to be reasonably designed in combination with the actual water quality.

[0020] Preferably, in step S2, the TiO2 / FTO is connected to a silicon cell, the TiO2 / FTO is obtained by hydrothermal calcination, and the 1T-2H MoS2 / GF is obtained by hydrothermally depositing 1T-2H phase MoS2 on a GF (graphite felt) electrode.

[0021] More preferably, in step S2, the TiO2 / FTO photoanode is prepared by spin-coating and calcination using deionized water, hydrochloric acid, and tetrabutyl titanate as precursors to prepare a seed layer, and then prepared by hydrothermal treatment.

[0022] More preferably, in step S2, the 1T-2H MoS2 / GF cathode is prepared by placing GF in a mixed solution of molybdenum trioxide, thioacetamide, and urea and hydrothermally treating it at 180°C - 240°C for 12 - 24 hours.

[0023] More preferably, in Cu@1T-2H MoS2 / GF, 1T-2H MoS2 refers to MoS2 that simultaneously has 1T phase and 2H phase, and the 1T phase and 2H phase are two main phase states of MoS2.

[0024] Preferably, in step S2, the light intensity of the xenon lamp is 80 - 120 mW / cm 2 , and the time for the complex dissociation reaction is 30 min - 120 min.

[0025] More preferably, in step S2, the light intensity of the xenon lamp is 100 mW / cm 2 (AM 1.5).

[0026] Preferably, in step S3, the temperature for vacuum drying is 60°C - 80°C, and the time is 8 - 16 h.

[0027] Preferably, in step S3, in the mixed atmosphere, the mixed volume ratio of nitrogen and oxygen is 3:1 to 5:1, the calcination temperature is 180 - 350°C, and the calcination time is 4 - 6 h.

[0028] Preferably, in step S4, the working voltage for electrochemical reduction is -0.8 to -1.2 V, and the time is 60 min - 120 min.

[0029] Preferably, in step S4, the three-electrode system refers to using Cu@1T-2H MoS2 / GF as the working electrode, SCE (saturated calomel electrode) as the reference electrode, and a graphite electrode as the counter electrode.

[0030] Preferably, in step S5, the standing time is 1 - 2 h, and the filtration refers to filtering the electrolyte after the reaction through a filter membrane, and the specification of the filter membrane is 0.22 μm - 0.45 μm.

[0031] Preferably, after recovering metallic Cu, the content of copper ions in the electroplating wastewater is below 0.01 mg / L, and the purity of the obtained high-purity EDTA solution is 60%-80%.

[0032] The present invention also provides an application of a high-purity EDTA solution prepared by a closed-loop process for realizing the synchronous recycling of high-efficiency metal recovery and complex ligand in electroplating wastewater. The recovered high-purity EDTA solution can be used as an eluent for heavy metal-contaminated soil.

[0033] Preferably, the soil is collected from a non-ferrous metal smelter, and the soil texture is loamy clay.

[0034] A closed-loop process for realizing the high-efficiency metal recovery and complex ligand recycling in electroplating wastewater provided by the present invention is divided into two parts: high-efficiency metal recovery and complex ligand regeneration and recycling. Taking the wastewater containing Cu(II)-EDTA as an example, first, a photoelectrocatalytic reaction system with a self-driven TiO2 photoanode and a 1T-2H MoS2 / GF photocathode is constructed. The wastewater containing Cu(II)-EDTA is added to the photoelectrochemical reaction cell, and an appropriate amount of sodium bicarbonate is added and the pH is adjusted to 7.5-8.5. The bicarbonate is activated by the holes separated by the photoanode to generate carbonate radicals to participate in the complex dissociation reaction. At the same time, the bicarbonate serves as an endogenous inhibitor to capture the non-selective radicals generated in the reaction, thereby controlling the selectivity of the complex dissociation reaction to ensure that Cu(II) (Cu 2+ ) is reduced and deposited on the cathode while the framework structure of the EDTA ligand can be retained; the recovered cathode is calcined in a gas atmosphere mixed with nitrogen and oxygen as the working electrode, and the reduction reaction of EDTA is carried out in a three-electrode electrolytic cell. After electrochemical carboxylation and proton-coupled electron transfer (PCET) reduction of the imino group, a high-purity EDTA solution is finally obtained; by comparing the performance of the recovered EDTA and commercially available EDTA in the elution ability of heavy metal-contaminated soil, the recovered EDTA can basically reach the elution ability of commercially available EDTA, realizing the integrated design of "complex dissociation-recovery-regeneration".

[0035] The complex dissociation reaction in the present invention is specifically as follows:

[0036] 1) TiO2 + hv → h + + e - ;

[0037] 2) h + + HCO3 - → CO3 ·- + H2O;

[0038] 3) HCO4 - + H2O → HCO3 -+H2O2;

[0039] 4) H2O2 + e - → OH · + H2O;

[0040] 5) 2H + + O2 + 2e - → H2O2 (2 - photon process);

[0041] 6) · OH + HCO3 - → H2O + ·CO3 - ;

[0042] 7) · OH + CO3 - → OH - + CO3 - ·;

[0043] 8) H2O2 + ·CO3 - → HCO3 - + HO2·;

[0044] 9) ·CO3 - + HO2 - → ·O2 - + HCO3 - ;

[0045] The technical principle of the present invention is as follows:

[0046] (1) The carbonate radical (CO3 ·- ) is an electrophilic radical that can selectively react with the electron - rich centers of compounds (such as the N - containing part). In addition, the lifetime of CO3 ·- is three orders of magnitude longer than that of ordinary radicals (such as hydroxyl and chlorine radicals). Relevant literature has reported that CO3 ·- can fully attack the electron - rich amino group of Cu(II) - EDTA, realizing the rapid decarboxylation of the metal complex and releasing metal ions. On this basis, the present invention uses a photoelectrocatalytic technology combined with carbonate radicals to decomplex Cu(II) - EDTA - containing wastewater. While the Cu(II) - EDTA is being decomplexed in the photoelectrochemical reaction system, the cathode simultaneously reduces and recovers the released free copper. By increasing the dosage of bicarbonate (10 mM), the hydroxyl radicals and superoxide radicals inevitably generated in the reaction are quenched, so that the carbonate radical becomes the active substance leading the reaction. By controlling the reaction conditions, while decomplexing Cu(II) - EDTA and completely recovering Cu, the basic framework (IMDA) of the ligand EDTA is retained, providing favorable conditions for subsequent reduction and recovery.

[0047] (2) Electrochemical reduction usually acts on the electrodes in the reaction system through current or voltage, thereby initiating a reduction reaction. In the electrochemical reduction reaction, the surface of the electrode adsorbs electrons and provides a reducing agent, causing the target substance to undergo a reduction reaction. The main conditions for the dominant reaction are the electrolyte, the working electrode, and the working potential. Using the recovered cathode in the dissociation section as a substrate, a Cu@1T-2H MoS2 / GF electrode with high catalytic reaction activity was prepared. The surface of this electrode has a mixed valence state of Cu (0 valence, 1 valence, 2 valence), which is beneficial to the progress of the reduction reaction. From IMDA to EDTA, it mainly involves the introduction of carboxylic acid groups and the reduction of imino groups to amino groups. The core of the carboxylation reaction is to insert CO2 into the methylene (-CH2-) position of IMDA through electrochemical reduction to complete the missing carboxylic acid group (-CH2COO-). Bicarbonate (HCO3 - ) in the electrolyte is reduced to CO2 on the surface of the cathode, and CO2 is adsorbed on the surface of Cu nanoparticles to form an activated *CO2 - intermediate. At the same time, the methylene (-CH2-) of IMDA acts as a nucleophilic site to attack *CO2 - , forming a new C-C bond. This step needs to overcome an energy barrier of 0.8 eV (supported by DFT calculations). The Cu nanoparticles reduce the activation energy through d-orbital electron transfer. The reduction of the imino group (-NH-) is completed through Proton-Coupled Electron Transfer (PCET). H + in the electrolyte is adsorbed on the sulfur vacancies at the edge of MoS2, forming adsorbed H*. H* can combine with the imino group (-NH-) to form an intermediate (-NH2 - ), which completes protonation and electron injection. Then, through the injection of conduction band electrons of MoS2, the intermediate (-NH2 - ) is further reduced to an amino group (-NH2), completing the transformation of the imino group to an amino group.

[0048] The present invention uses photo-electrocatalytic drive to synergistically degrade Cu(II)-EDTA wastewater with carbonate radicals. While effectively separating and recovering Cu, it retains the framework structure of the organic ligand. The EDTA is in-situ regenerated and recovered by using electrochemical reduction technology. At the same time, the treatment process does not require complex equipment, has a low operating cost, and is easy to realize engineering applications.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) A closed-loop process provided by the present invention for realizing the efficient metal recovery of electroplating wastewater and the synchronous recycling of complex ligands can simultaneously and efficiently recover copper ions and EDTA complex ligands. The recovery efficiency of copper ions is high, and the recovered EDTA complex ligand is a high-purity EDTA solution.

[0051] (2) The process of the present invention is applicable to wastewater containing Cu(II)-EDTA, with high efficiency in the dissociation of Cu(II)-EDTA, short reaction time, capable of completely recovering the copper ions released by dissociation, and the recovery efficiency of copper in the wastewater approaching 100%. The content of copper ions in the treated wastewater is below 0.01 mg / L.

[0052] (3) In terms of ligand recovery, the present invention first proposes a system for reducing and recovering EDTA based on photocatalytic electrocatalysis, providing a new path for the resource treatment of wastewater in the future.

[0053] (4) The high-purity EDTA solution recovered by the present invention still has excellent complexing ability, can be used as an eluent for heavy metal contaminated soil, has good removal effects on As, Sb, Cu, Ni and Cr in the soil, and can basically reach the elution ability of commercially available EDTA. The EDTA recovered by the present invention has extremely high market economic value.

[0054] (5) The operation of the present invention is simple, the process flow is simple, no additional oxidation complexing agent is required, which conforms to the concept of green sustainable development; the present invention is carried out at pH = 7.5 - 8.5, does not have a high pH dependence, does not require complex equipment during the treatment process, has a low operation cost, and is easy to apply during the process.

[0055] (6) The present invention has strong anti-interference ability. Common anions and cations in the wastewater such as NO3 - , Cl - , NH4 + etc. have no obvious influence on the dissociation performance of the system constructed by the present invention.

[0056] (7) Through the integrated design of "dissociation - recovery - regeneration", the present invention transforms the heavy metal complex wastewater from an environmental burden into a resource carrier, providing an innovative paradigm for industrial wastewater treatment and soil remediation. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 : Working principle diagram of the invention;

[0058] Figure 2 : Comparison of the dissociation performance of Cu(II)-EDTA in different systems at an initial pH = 8.0;

[0059] Figure 3 : Electron paramagnetic resonance spectrum of the system at an initial pH = 8.0 and n(HCO3 - ) = 4 mM;

[0060] Figure 4: Comparison of the complex dissociation performance of Cu(II)-EDTA in systems with different sodium bicarbonate dosages at an initial pH = 8.0;

[0061] Figure 5 : Electron paramagnetic resonance spectra of the system at an initial pH = 8.0 and n(HCO3 - ) = 10 mM;

[0062] Figure 6 : Mass spectra of the recovered liquid product after the complex dissociation reaction;

[0063] Figure 7 : Comparison of the infrared spectra of the liquid in the reaction tank before and after the complex dissociation reaction;

[0064] Figure 8 : Comparison of the infrared spectra of the products at different reaction times in the electrolytic cell at an initial pH = 5.5 and a working voltage of -1 V;

[0065] Figure 9 : Raman spectra of the recovered EDTA after filtration treatment;

[0066] Figure 10 : Influence of common anions and cations in wastewater on the complex dissociation performance of the system in a system with an initial pH = 8.0, and initial concentrations of NaHCO3 and Cu(II)-EDTA of 10 mM and 1 mM respectively;

[0067] Figure 11 : Comparison of the elution ability of the recovered EDTA and commercially available EDTA for common metal ions in soil. Detailed implementation mode

[0068] This embodiment is implemented on the premise of the technical solution of the present invention, and gives detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0069] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0070] A closed-loop process for realizing efficient metal recovery from electroplating wastewater and synchronous recycling of complex ligands, as Figure 1 shown, constructs a photoelectrocatalytic reaction system with TiO2 / FTO as the photoanode and 1T-2H MoS2 / GF as the photocathode. Through photoelectrocatalysis, bicarbonate is driven to generate carbonate radicals, degrade Cu(II)-EDTA in electroplating wastewater, recover metallic Cu, and use electrochemical reduction technology to in-situ regenerate and recover EDTA. The specific steps are as follows:

[0071] S1: Add sodium bicarbonate to the electroplating wastewater containing Cu(II)-EDTA and adjust the pH to obtain an electrolyte solution.

[0072] S2: Using TiO2 / FTO as the photoanode, 1T-2H MoS2 / GF as the photocathode, and a xenon lamp as the light source, perform a complex dissociation reaction on the electrolyte solution in step S1 to reduce and deposit Cu(II) on the photocathode, thereby recovering metallic Cu.

[0073] S3: Clean the photocathode deposited with Cu(II) obtained in step S2 and perform vacuum drying. Subsequently, calcine it in a mixed atmosphere containing nitrogen and oxygen to prepare Cu@1T-2H MoS2 / GF.

[0074] S4: Construct a three-electrode system, using Cu@1T-2H MoS2 / GF obtained in step S3 as the working electrode to perform electrochemical reduction.

[0075] S5: After the reduction reaction is completed, let it stand and filter to recover a high-purity EDTA solution.

[0076] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0077] Example 1: Recovery of copper ions in the PEC / NaHCO3 system

[0078] Refer to the actual properties of Cu(II)-EDTA wastewater to prepare a simulated reaction solution with an initial concentration of Cu(II)-EDTA of 4 mMol / L. Using TiO2 / FTO as the photoanode and 1T-2H MoS2 / GF as the cathode to construct a two-electrode system (PEC system), and add 4 mM NaHCO3 to evaluate the degradation ability of the PEC / NaHCO3 system. The TiO2 / FTO photoanode is prepared by spin-coating and calcining using deionized water, hydrochloric acid, and tetrabutyl titanate as precursors to prepare a seed layer, and then prepared by hydrothermal method. The 1T-2H MoS2 / GF cathode is prepared by placing GF in a mixed solution of molybdenum trioxide, thioacetamide, and urea and performing hydrothermal treatment at 180°C - 240°C for 12 - 24 hours. The light intensity of the light source is 100 mW / cm 2 , and the time is 30 minutes.

[0079] All experiments are carried out in a quartz reactor containing 200 ml of 1 mM Cu(II)-EDTA solution, with an initial pH value of 8.0. During the entire degradation process, samples are extracted from the reaction vessel every 5 minutes for analysis. The residual level of Cu(II)-EDTA during the degradation process is determined by ultra-high performance liquid chromatography with a retention time of 7.5 minutes. All experiments are repeated at least three times, and the measurement results are presented as graphs with error bars.

[0080] Comparative Example 1: Recovery of copper ions in the NaHCO3 system

[0081] The experiment was carried out in a quartz reactor containing 200 ml of simulated solution, and the initial pH value was 8.0. Only 4 mM of NaHCO3 was added to the reactor, and the reaction was allowed to stand for 30 minutes. The dissociation efficiency of Cu(II)-EDTA and the recovery of Cu were analyzed.

[0082] Comparative Example 2: Recovery of copper ions in the PEC system

[0083] A PEC system was constructed with TiO2 / FTO as the photoanode and 1T-2H MoS2 / GF as the cathode. The experiment was carried out in a quartz reactor containing 200 ml of simulated solution, and the initial pH value was 8.0. The simulated light source was turned on, and the reaction was irradiated for 30 minutes. The dissociation efficiency of Cu(II)-EDTA and the recovery of Cu were analyzed.

[0084] Comparative Example 3: Recovery of copper ions in the PEC / H2O2 system

[0085] A PEC system was constructed with TiO2 / FTO as the photoanode and 1T-2H MoS2 / GF as the cathode. 4 mM of hydrogen peroxide was added to the quartz reactor containing 200 ml of simulated solution, and the initial pH value was 8.0. The simulated light source was turned on, and the reaction was irradiated for 30 minutes. The dissociation efficiency of Cu(II)-EDTA and the recovery of Cu were analyzed.

[0086] The experimental results of Example 1 and Comparative Examples 1-3 are as Figure 2 shown. At the initial pH = 8.0, Cu(II)-EDTA had no obvious removal effect in the single NaHCO3 system, and the PEC process achieved a dissociation performance of 60.1% within 30 minutes. Compared with the PEC / H2O2 process, PEC / NaHCO3 could achieve complete dissociation of Cu(II)-EDTA within 30 minutes. After standing for 1 hour, the concentration of copper ions in the solution was below the detection limit of the instrument (<0.01 mg / L).

[0087] Electron paramagnetic resonance (EPR) was used to analyze the active species in the PEC / NaHCO3 system. As Figure 3 shown, the adduct signal peaks corresponding to DMPO- · OH, DMPO-O2 ·- , and DMPO-CO3 ·- were detected in the PEC / NaHCO3 system, preliminarily confirming that · OH, · O2 - , and CO3 ·- were the main active species.

[0088] Under the condition of initial pH = 8.0, by increasing the dosage of bicarbonate, which acts as an endogenous inhibitor to capture the generated · OH and · O2 - , thus avoiding the complete destruction of the EDTA structure and being able to retain the main framework. The comparison of the influence of different sodium bicarbonate dosages on the complex dissociation performance is as shown in Figure 4 . It can be found that during the process of gradually increasing the dosage from 4 mM to 10 mM, the complex dissociation performance of Cu(II)-EDTA is not inhibited. Using electron paramagnetic resonance to detect the active species in the system with a dosage of 10 mM, as shown in Figure 5 , it can be found that after reacting for 10 minutes, the peaks attributed to · OH and · O2 - gradually disappear, indicating that at this time CO3 ·- becomes the main active substance.

[0089] When the initial pH = 8.0 and n(HCO3 - ) = 10 mM, after waiting for the complex dissociation reaction to complete, let it stand for 1 hour, collect the liquid product in the reaction pool, filter it through a 0.22 μm filter membrane, and then analyze the main components of the liquid product by mass spectrometry. The mass spectrometry diagram is as shown in Figure 6 . The liquid product is mainly iminodiacetic acid (IMDA), and there are no small molecule acids generated after further oxidation.

[0090] Under the reaction conditions of initial pH = 8.0 and n(HCO3 - ) = 10 mM, use FTIR spectroscopy to analyze the changes in the solution before and after the reaction, and the results are as shown in Figure 7 . Comparing before and after the reaction, the carboxylic acid peak (~1700 cm -1 ) disappears, and the imino peak (~1580 cm -1 ) appears, providing strong evidence for the generation of IMDA.

[0091] Example 2: Recycling of EDTA

[0092] (1) Calcinate the cathode recycled in Example 1 under a mixed atmosphere of nitrogen and oxygen, with the mixing ratio of nitrogen and oxygen being 4:1, and calcinate at 200 °C for 4 hours. The new working electrode is named Cu@1T-2H MoS2 / GF.

[0093] (2) Use Cu@1T-2H MoS2 / GF as the working electrode, SCE as the reference electrode, and graphite electrode as the counter electrode to construct a three-electrode system for electrochemical reduction. The reaction is carried out under the conditions of initial pH = 5.5 and working voltage of -1 V to recycle EDTA.

[0094] The infrared spectra of the reaction solution were monitored by FTIR at 0 min, 30 min, and 60 min respectively, and the results are as Figure 8 shown. As the reaction time progresses, the carboxylic acid peak corresponding to EDTA (1700 cm -1 ) slowly recovers, while the imino peak gradually (1580 cm -1 ) disappears, and the amino peak (1600 cm -1 ) begins to slowly increase. After the reaction ends, it is characterized by Raman spectroscopy after filtration and recovery. As Figure 9 shown, the recovered solution is high-purity EDTA.

[0095] In a system with an initial pH = 8.0, and the initial concentrations of NaHCO3 and Cu(II)-EDTA being 10 mM and 1 mM respectively, the effects of common cations and anions in wastewater on the complex dissociation performance of the system were studied. The results are as Figure 10 shown. The coexisting cations and anions have no obvious inhibitory effect. The results indicate that this process has strong interference resistance.

[0096] Application Example 1

[0097] An eluent with the same concentration as the recovered EDTA in Example 2 was prepared using commercially available EDTA, and the solution pH = 5. The removal effects of the recovered EDTA and fresh commercially available EDTA on As, Sb, Cu, Ni, and Cr in soil were compared. The results are as Figure 11 shown. The removal ability of the recovered EDTA is not much different from that of fresh EDTA, which indicates that the recovered EDTA still has excellent complexing ability and extremely high market economic value.

[0098] In summary, based on the photo-electrocatalytic synergistic carbonate radical method and the Cu@1T-2H MoS2 / GF electrochemical reduction process, the present invention can achieve the degradation of metal complex-containing wastewater and the efficient recovery of metals and ligands. Taking Cu(II)-EDTA as an example, after conversion, the recovery efficiency of copper in the wastewater is close to 100%, the content of copper ions in the treated wastewater is below 0.01 mg / L, and the recovered solution is a high-purity EDTA solution. Using this high-purity EDTA solution as the eluent for heavy metal-contaminated soil, it can basically achieve the elution ability of commercially available EDTA. Through the integrated design of "complex dissociation - recovery - regeneration", the present invention transforms heavy metal complex-containing wastewater from an environmental burden into a resource carrier, providing an innovative paradigm for industrial wastewater treatment and soil remediation.

[0099] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands in electroplating wastewater, characterized in that, Construct a photoelectrocatalytic reaction system with TiO2 / FTO as the photoanode and 1T-2H MoS2 / GF as the photocathode. Drive the generation of carbonate radicals from bicarbonate through photoelectrocatalysis to degrade Cu(II)-EDTA in electroplating wastewater, recover metallic Cu, and in-situ regenerate and recover EDTA using electrochemical reduction technology. The specific steps are as follows: S1: Add sodium bicarbonate to the electroplating wastewater containing Cu(II)-EDTA and adjust the pH to obtain an electrolyte solution. S2: Using TiO2 / FTO as the photoanode, 1T-2H MoS2 / GF as the photocathode, and a xenon lamp as the light source, perform a complex dissociation reaction on the electrolyte solution in step S1 to reduce and deposit Cu(II) on the photocathode, thereby recovering metallic Cu. S3: Wash the photocathode deposited with Cu(II) obtained in step S2 and dry it under vacuum. Subsequently, calcine it in a mixed atmosphere of nitrogen and oxygen to prepare Cu@1T-2H MoS2 / GF. S4: Construct a three-electrode system, using Cu@1T-2H MoS2 / GF obtained in step S3 as the working electrode, and perform an electrochemical reduction reaction on the electrolyte solution that has undergone the complex dissociation reaction and recovered metallic Cu in step S2. S5: After the reduction reaction is completed, let it stand and filter to recover a high-purity EDTA solution.

2. The closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands in electroplating wastewater according to claim 1, characterized in that, In step S1, the concentration of Cu(II)-EDTA in the electrolyte solution is 0.1 mM - 1 mM, the concentration of sodium bicarbonate in the electrolyte solution is 1 - 20 mM, and the pH is adjusted to 7.5 - 8.

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3. A closed-loop process for efficiently recycling metals and synchronously recycling complex ligands from electroplating wastewater according to claim 1, characterized in that, In step S2, the TiO2 / FTO is connected to a silicon solar cell. The TiO2 / FTO is obtained through a hydrothermal calcination process, and the 1T-2H MoS2 / GF is obtained by depositing 1T-2H phase MoS2 on a GF electrode through a hydrothermal method.

4. A closed-loop process for efficiently recycling metals and simultaneously recycling complex ligands from electroplating wastewater according to claim 1, characterized in that, In step S2, the illumination intensity of the light source is 80 - 120 mW / cm 2 , and the time of the dissociation reaction is 30 min - 120 min.

5. A closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands in electroplating wastewater according to claim 1, characterized in that, In step S3, the temperature of the vacuum drying is 60°C - 80°C, and the time is 8 - 16 h.

6. A closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands from electroplating wastewater according to claim 1, characterized in that, In step S3, in the mixed atmosphere, the volume ratio of nitrogen to oxygen is 3:1 - 5:1, the calcination temperature is 180 - 350°C, and the calcination time is 4 - 6 h.

7. A closed-loop process for efficiently recycling metals and synchronously recycling complex ligands from electroplating wastewater according to claim 1, characterized in that, In step S4, the working voltage of the electrochemical reduction is -0.8 - -1.2 V, and the time is 60 min - 120 min.

8. A closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands from electroplating wastewater according to claim 1, characterized in that, In step S5, the standing time is 1 - 2 h. The filtration refers to filtering the electrolyte solution after the reaction is completed through a filter membrane, and the specification of the filter membrane is 0.22 μm - 0.45 μm.

9. A closed-loop process for realizing the synchronous recycling of highly efficient metal recovery and complex ligands in electroplating wastewater according to claim 1, characterized in that, After recovering metallic Cu, the copper ion content in the electroplating wastewater is below 0.01 mg / L, and the purity of the obtained high-purity EDTA solution is 60% - 80%.

10. Use of a highly pure EDTA solution obtained by a closed-loop process for realizing efficient metal recovery from electroplating wastewater and synchronous recycling of complex ligands as described in any one of claims 1-9, characterized in that, The recovered high-purity EDTA solution can be used as an eluent for heavy metal contaminated soil.

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