Reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater by pulsed voltage

Abstract

The present invention provides a reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater through pulsed voltage, belonging to the field of electrochemical technology. The reaction method comprises the following steps: The reaction method uses two electrochemical workstations and a reactor containing a first cathode, a second cathode, an anode, and a reference electrode; when one electrochemical workstation provides a pulsed voltage to the first cathode or the second cathode, the other electrochemical workstation provides a constant voltage to the remaining cathode; during the reaction process, air or oxygen is continuously introduced into the reaction solution in the reactor. The dual-cathode electro-Fenton-like system proposed by the present invention does not require the addition of Fe 2+ or any chemical reagent, and the oxidant H2O2 is in-situ generated by the reduction of dissolved oxygen at the cathode, and the activation of H2O2 is induced by the intermediate products electro-oxidized and degraded at the anode - low coordination number heavy metal complexes or ionic heavy metals.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemistry, and in particular relates to a reaction method for enhancing the removal of heavy metal complexes and directional recovery of heavy metals in wastewater by pulse voltage. Background Art

[0002] Electronic electroplating, metal smelting, leather making and other industries will produce a large amount of heavy metal wastewater. Once heavy metals enter surface water, soil and groundwater and enter the human body through the enrichment of the food chain, they will seriously threaten human health. Electroplating wastewater is the main source of heavy metal wastewater. A large amount of chelating agents (such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, citric acid and tartaric acid, etc.) are also used in electroplating production. These chelating agents will form heavy metal complexes with heavy metal ions. The complexes have a stable chemical structure and are difficult to degrade naturally. Traditional chemical precipitation, adsorption and coagulation technologies can effectively remove ionic heavy metals, but the removal efficiency of complexed heavy metals is low. At the same time, heavy metals are also a valuable resource, and their resource recovery is increasingly valued. Therefore, the development of efficient resource treatment technology for heavy metal complex wastewater has important practical significance for ecological environmental protection and the healthy and sustainable development of the electroplating industry.

[0003] Electrochemical water treatment technology usually refers to the degradation of pollutants in water by applying current or voltage to cause electrons to move in a directional manner, thereby causing redox reactions on the electrode surface. Compared with traditional chemical methods, electrochemical technology requires significantly less reagents and discharges less sludge, and has the advantages of fast reaction rate, mild reaction conditions, and easy automation. Electro-Fenton can produce H2O2 in situ by reducing O2 at the cathode, and the addition of metal ions or heavy metals (complexes) existing in the water induce (quasi-) Fenton reactions to produce oxidative free radicals. It is a relatively green and safe advanced oxidation technology. When the traditional single-cathode electrochemical system treats heavy metal complex wastewater, due to the large amount of heavy metals deposited on the cathode, it will inhibit the two-electron ORR (Oxidation-Reduction Reaction) process on the electrode surface, and cannot effectively achieve simultaneous electroproduction of H2O2 and recovery of heavy metals. Summary of the invention

[0004] The present invention proposes a reaction method for enhancing the removal of typical heavy metal complexes and directional recovery of heavy metals in wastewater by pulse voltage, a dual cathode electro-Fenton system is used to treat heavy metal complexes, and two electrochemical workstations are used to connect two cathodes, an anode, and a reference electrode respectively. The electrochemical workstation is used to provide a pulse voltage to one of the cathodes to improve the oxidation and decomposition ability of heavy metal complexes (such as Cu-EDTA) and the directional recovery efficiency of heavy metals (such as Cu).

[0005] The present invention provides a reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater through pulsed voltage, which includes the following steps:

[0006] The reaction method uses two electrochemical workstations and a reactor containing a first cathode, a second cathode, an anode, and a reference electrode; when one electrochemical workstation provides a pulsed voltage for the first cathode or the second cathode, the other electrochemical workstation provides a constant voltage for the remaining cathode.

[0007] During the reaction process, air or oxygen is continuously introduced into the reaction solution in the reactor.

[0008] Further, the first cathode is carbon aerogel, carbon fiber, or carbon felt;

[0009] Preferably, the first cathode is carbon aerogel.

[0010] Further, the second cathode is a titanium plate or stainless steel;

[0011] Preferably, the second cathode is a titanium plate.

[0012] Further, the pulsed voltage includes a square wave pulsed voltage, a triangular pulsed voltage, or a differential pulsed voltage.

[0013] Further, the range of the pulsed voltage is: 0 to -2.0 V;

[0014] Preferably, the range of the pulsed voltage of the first cathode is 0 to -1.5 V, and the range of the pulsed voltage of the second cathode is 0 to -2.0 V;

[0015] More preferably, on the first cathode, the voltage range of the square wave pulse is 0 to -0.9 V, the voltage range of the triangular pulse is -0.6 to -0.9 V, and the voltage range of the differential pulse is -0.6 to -0.9 V;

[0016] On the second cathode, the voltage range of the square wave pulse is 0 to -1.35 V, the voltage range of the triangular pulse is -1.05 to -1.35 V, and the voltage range of the differential pulse is -1.05 to -1.35 V.

[0017] Further, the duty cycle of the square wave pulsed voltage is 0 - 300%;

[0018] Preferably, the duty cycle of the square wave pulsed voltage on the first cathode is 100%, and the duty cycle of the square wave pulsed voltage on the second cathode is 100%.

[0019] Further, the pulse width of the pulsed voltage is 0 to 60 s;

[0020] Preferably, the pulse width of the first cathode is 2.5 to 10 s, and the pulse width of the second cathode is 5 to 15 s.

[0021] Further, in the constant voltage, the constant voltage of the first cathode is -0.6 to -1.5 V, and the constant voltage of the second cathode is -0.8 to -2.0 V;

[0022] Preferably, in the constant voltage, the constant potential of the first cathode is -0.90 V; the constant potential of the second cathode is -1.35 V.

[0023] Further, the anode is a titanium ruthenium iridium mesh; the reference electrode is an Ag / AgCl electrode.

[0024] Further, the first cathode, the second cathode and the anode are arranged parallel to each other.

[0025] The present invention has the following advantages:

[0026] The reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater by pulsed voltage proposed by the present invention uses a dual-cathode electro-Fenton system to treat heavy metal complexes, effectively enhancing the oxidative breaking of heavy metal complexes and achieving the directional recovery of heavy metals. Moreover, two electrochemical workstations are used to connect two cathodes (the first cathode and the second cathode), a reference electrode, and an anode respectively. According to the actual wastewater quality, different pulsed voltage modes are applied to one of the first cathode or the second cathode. The first cathode in-situ generates H2O2 through a two-electron ORR reaction, which is activated by the complexed or ionic heavy metals in the heavy metal wastewater to induce a Fenton-like reaction. The second cathode then directionally recovers the released Cu ions, further enhancing the breaking and degradation of heavy metal complexes and the directional recovery of heavy metals in the dual-cathode system. This method can achieve the directional recovery of heavy metals while efficiently removing heavy metal complexes from wastewater, without adding external Fe 2+ or any chemical agents, and by applying a pulsed voltage mode, the electrodes will intermittently be in a non-working or low-voltage state, which can reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 is a schematic structural diagram of a dual-cathode electrochemical reaction device in an embodiment of the present invention;

[0029] 1(2)-electrochemical workstation; 3-first cathode; 4-second cathode; 5-anode; 6-reference electrode;

[0030] Figure 2 Schematic diagram of the square wave pulse voltage applied to the first cathode in Embodiment 1 of the present invention;

[0031] Figure 3 Schematic diagram of the square wave pulse voltage applied to the first cathode in Embodiment 2 of the present invention;

[0032] Figure 4 Schematic diagram of the triangular pulse voltage applied to the first cathode in Embodiment 3 of the present invention;

[0033] Figure 5 Schematic diagram of the differential pulse voltage applied to the first cathode in Embodiment 4 of the present invention;

[0034] Figure 6 (a) In Embodiment of the present invention, Cu-EDTA degrades to produce low-coordination complexes such as Cu-IDA and Cu-EDDA, Figure 6 (b) Test diagram with stronger ·OH signal generated by activating H2O2 with low-coordination copper complexes in the embodiment of the present invention;

[0035] Figure 7 Comparison effect diagram of the electroreduction of the second cathode and the first cathode to generate Cu(I) in the embodiment of the present invention;

[0036] Figure 8 Comparison effect diagram of in-situ Cu(III) generation between the dual-cathode and single-cathode systems in the embodiment of the present invention. Detailed implementation manners

[0037] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0038] An embodiment of the present invention provides a reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater by pulse voltage, comprising the following steps:

[0039] The reaction method uses two electrochemical workstations and a reactor containing a first cathode, a second cathode, an anode, and a reference electrode; when one electrochemical workstation provides a pulse voltage for the first cathode or the second cathode, the other electrochemical workstation provides a constant voltage for the remaining cathode;

[0040] During the reaction process, air or oxygen is continuously introduced into the reaction solution in the reactor.

[0041] In the embodiments of the present invention, a dual-cathode electro-Fenton-like system is used to treat heavy metal complexes. At the first cathode, hydroxyl radicals generated by the anode can be utilized to electro-oxidize and degrade the low-coordination-number copper complexes produced by Cu-EDTA, and these low-coordination-number Cu complexes have better ability to activate H2O2 to generate ·OH, thereby realizing self-enhanced complex-breaking; the second cathode can electro-reduce to generate Cu(I), further promoting the activation of H2O2 to generate ·OH. At the same time, compared with the single-cathode system, the dual-cathode system promotes the generation of Cu(III), because the H2O2 in-situ generated at the first cathode can react with the Cu(I) generated by the reduction of Cu(II) at the second cathode to generate Cu(III), and Cu(III) has strong oxidation ability, which can strengthen the oxidation and complex-breaking of heavy metal copper complexes.

[0042] In the embodiments of the present invention, two electrochemical workstations are used to connect two cathodes (the first cathode, the second cathode), a reference electrode, and an anode respectively. According to the actual wastewater quality, different pulse-mode voltages are applied to one of the first cathode or the second cathode to realize the enhancement of the complex-breaking degradation of heavy metal complexes and the directional cathode recovery of heavy metals in the dual-cathode system. Among them, the first cathode in-situ generates H2O2 through a two-electron ORR reaction, which is activated by the complexed or ionic heavy metals in the heavy metal wastewater to induce a Fenton-like reaction, and the second cathode directionally recovers the released Cu ions (or can also reduce to generate monovalent copper to promote the activation of H2O2 and finally recover in the form of elemental copper).

[0043] In the reaction method proposed by the embodiments of the present invention, no external Fe 2+ or any chemical reagent is required. The oxidant H2O2 is in-situ generated by the reduction of dissolved oxygen at the first cathode, and the activation of H2O2 is induced synergistically by the low-coordination-number copper complexes, ionic copper, and the transition-state monovalent copper on the second cathode, which are the intermediate products of the anodic electro-oxidation of Cu-EDTA. Moreover, when a pulse-mode voltage is applied, the electrodes will intermittently be in a non-working or low-voltage state, which can also reduce energy consumption.

[0044] In one embodiment of the present invention, the first cathode is carbon aerogel (CA, carbon aerogels), carbon fiber or carbon felt. Preferably, the first cathode is carbon aerogel.

[0045] In one embodiment of the present invention, the second cathode is a titanium (Ti) plate or stainless steel. Preferably, the second cathode is a titanium plate.

[0046] It should be noted that in the embodiments of the present invention, the two electrochemical workstations are electrochemical workstations with the same function. According to needs, the electrochemical workstation can provide a pulsed voltage or a constant voltage. The first cathode is connected to one of the electrochemical workstations, and the second cathode is connected to the other electrochemical workstation. When the first cathode receives the pulsed voltage provided by the connected electrochemical workstation, the second cathode will receive the constant voltage provided by the connected electrochemical workstation. The anode is connected to both electrochemical workstations and is shared by the two electrochemical workstations. The reference electrode is connected to both electrochemical workstations and is shared by the two electrochemical workstations (see Figure 1 ).

[0047] In the embodiments of the present invention, the pulsed voltage mode provides a pulsed voltage during the electrolysis process, and the current and charge will change differently according to the specific situation of the pulse. Compared with the constant potential, the pulsed voltage can dynamically disturb the electrode-liquid interface to promote the diffusion of ions and substances, reduce the concentration polarization of the electrochemical reaction, and is beneficial to the enrichment of the target substance and the diffusion of the product during the electrochemical reaction process.

[0048] The dual-cathode electrochemical reaction system proposed in the embodiments of the present invention, during the treatment of heavy metal complex wastewater, by setting two electrochemical workstations, applying different modes of pulsed voltage to any cathode in the dual-cathode system, by applying different pulsed voltages to the first cathode, the yield of H2O2 at the first cathode is increased, and the ability of the system to break the complex is further enhanced. By applying different pulsed voltages to the second cathode, the proportion of Cu recovered at the second cathode is increased, and the directional recovery of Cu is achieved.

[0049] The first cathode reduces the dissolved oxygen in water to H2O2 through a 2e- oxygen reduction reaction. By applying a pulsed voltage to the first cathode, the first cathode alternately undergoes a Faraday process and a non-Faraday process, which can promote the diffusion of dissolved oxygen on the surface of the first cathode, continuously replenish the dissolved oxygen on the electrode surface, and improve the efficiency of in-situ electrochemically generating H2O2 at the first cathode. The H2O2 generated by the first cathode undergoes a Fenton-like reaction with the heavy metal complex (intermediate product) in the wastewater to generate hydroxyl radicals, and synergistically with the electrooxidation of the anode to strengthen the breaking of the Cu complex. After the Cu complex is completely broken, it will be released into the solution to form free Cu ions.

[0050] After applying a pulsed potential to the second cathode, by applying a pulsed voltage to the second cathode, the ability of the electrode to directionally recover free copper ions in the solution is enhanced. By applying different pulsed voltages to the second cathode, the H + existing at the cathode can diffuse into the electrolyte solution in time, inhibit the hydrogen evolution reaction on the electrode surface, provide more active sites for the reduction of Cu on the cathode surface, and solve the problem of the small proportion of heavy metals recovered by the second cathode.

[0051] Specifically, the chemical reactions occurring in the dual-cathode electro-Fenton-like system are as follows:

[0052] First cathode: The cathode accepts electrons through 2e - The oxygen reduction reaction reduces dissolved oxygen in water to H2O2. The specific reaction formula is:

[0053] O2 + 2H + + 2e - → H2O2 (1);

[0054] H2O2 will react with copper complexes in the solution, especially low-coordination-number copper complexes (Cu-EDTA produces low-coordination-number copper complexes such as Cu-EDDA and Cu-IDA under the oxidation of hydroxyl radicals generated at the anode. Compared with the initial Cu-EDTA saturated ligand complex, the low-coordination-number copper complex has a stronger ability to activate H2O2 to produce ·OH. See Figure 6 a and 6b), or Cu 2+ A Fenton-like reaction occurs. The specific reaction formula is:

[0055] L-Cu(II) + H2O2 → L-Cu(I) +·OOH + H + (2);

[0056] L-Cu(I) + H2O2 → L-Cu(II) +·OH + OH - (3);

[0057] Cu 2+ + H2O2 → Cu + + ·OOH + H + (4);

[0058] Cu + + H2O2 → Cu 2+ + ·OH + OH - (5);

[0059] Second cathode: The cathode reduces Cu 2+ to Cu + or Cu 0 , and finally realizes the recovery of free Cu ions in the solution at the second cathode. The specific reaction formula is:

[0060] Cu 2+ + 2e - → Cu 0 (6);

[0061] Cu 2+ + e - → Cu+ (7);

[0062] Cu + + e - → Cu 0 (8);

[0063] The second cathode can increase the production of Cu(I) (see Figure 7 ), and Cu(I) can promote the activation of H2O2 to produce ·OH. In addition, the H2O2 in-situ generated at the first cathode can react with the Cu(I) reduced from Cu(II) at the second cathode to form Cu(III). Therefore, compared with the single-cathode system, the dual-cathode system promotes the production of Cu(III) (see Figure 8 ), and Cu(III) has strong oxidation ability and can strengthen the oxidation and breaking of copper complexes.

[0064] Cu(I) + H2O2 → Cu(III) + 2OH - (9);

[0065] Anode: The reaction between the surface of metal oxide M and the adsorbed water molecules generates hydroxyl radicals, and the specific reaction formula is:

[0066] M + H2O → M(·OH) + H + + e - (10).

[0067] In one embodiment of the present invention, the pulsed voltage includes a square-wave pulsed voltage, a triangular pulsed voltage, or a differential pulsed voltage. It should be noted that the differential pulse refers to applying a series of positive and negative pulsed voltages on the electrode, with the same duration for both, and applying according to a specific pulse width.

[0068] In one embodiment of the present invention, the range of the pulsed voltage is: 0 to -2.0V.

[0069] Preferably, the range of the pulsed voltage of the first cathode is 0 to -1.5V, and the range of the pulsed voltage of the second cathode is 0 to -2.0V.

[0070] More preferably, on the first cathode, the voltage range of the square-wave pulse is 0 to -0.9V, the voltage range of the triangular pulse is -0.6 to -0.9V, and the voltage range of the differential pulse is -0.6 to -0.9V.

[0071] On the second cathode, the voltage range of the square-wave pulse is 0 to -1.35V, the voltage range of the triangular pulse is -1.05 to -1.35V, and the voltage range of the differential pulse is -1.05 to -1.35V.

[0072] In an embodiment of the present invention, the duty cycle of the square wave pulse voltage is 0 - 300%, and the duty cycle of the square wave pulse voltage is 0 - 300%; preferably, the duty cycle of the square wave pulse voltage above the first cathode is 100%, and the duty cycle of the square wave pulse voltage above the second cathode is 100%.

[0073] It should be noted that the duty cycle refers to the ratio of the energization time to the power-off time in a square wave pulse cycle.

[0074] In an embodiment of the present invention, the pulse width of the pulse voltage is 0 - 60 s. Preferably, the pulse width of the first cathode is 2.5 - 10 s, and the pulse width of the second cathode is 5 - 15 s.

[0075] In an embodiment of the present invention, in the constant voltage, the constant voltage of the first cathode is -0.6 to -1.5 V, and the constant voltage of the second cathode is -0.8 to -2.0 V. Preferably, the constant potential of the first cathode is -0.90 V; the constant potential of the second cathode is -1.35 V.

[0076] In the embodiment of the present invention, applying three pulse modes of square wave pulse, triangular pulse, and differential pulse on the first cathode can all promote the production of H2O2 by electrolysis. Among them, the square wave pulse voltage has a more significant effect on increasing the yield of H2O2, thereby promoting the oxidative complex breaking of Cu-EDTA. Preferably, when the pulse width of the square wave pulse is 5 s, the yield of H2O2 is the highest.

[0077] Specifically, the promotion of H2O2 generation in the dual-cathode system by the pulse voltage of the first cathode is mainly as follows: (1) The mass transfer of dissolved oxygen at the cathode is enhanced; (2) H2O2 at the cathode can be quickly diffused from the cathode surface to the bulk solution. When a constant potential is applied to the first cathode, the dissolved oxygen on the cathode surface is quickly consumed, resulting in a decrease in the interfacial dissolved oxygen concentration and a reduction in the reaction rate. At the same time, being in a high-current state for a long time will cause further electroreductive decomposition of H2O2. However, when a pulse voltage is applied to the first cathode, there will be a reaction process and a diffusion process at the first cathode. When the cathode is energized or a high potential is applied, the cathode consumes dissolved oxygen to produce H2O2. When the cathode is powered off or at a low potential, this is the diffusion stage, and the dissolved oxygen in the bulk solution will diffuse to the cathode surface again to make up for the consumption during the electrochemical reaction. This process occurs in the time range of seconds. Therefore, after applying a pulse voltage to the first cathode, the dissolved oxygen on the electrode surface can be continuously replenished, and the product H2O2 can be continuously diffused to the bulk solution, accelerating the entire electrode reaction process.

[0078] In the embodiments of the present invention, applying square wave pulses, triangular pulses, and differential pulses to the second cathode can all promote the directional recovery of Cu at the second cathode. Among them, the triangular pulse voltage has a more significant effect on the directional recovery of Cu. Preferably, when the pulse width is 10 s, the effect of the second cathode in directionally recovering Cu is the best.

[0079] Specifically, the way that the pulse voltage promotes the directional recovery of Cu in the dual-cathode system is mainly as follows: H + at the cathode can diffuse from the cathode surface into the electrolyte solution in a timely manner, providing more active sites for the reduction of Cu on the cathode surface, so that the second cathode obtains a better effect of directional recovery of Cu. When the second cathode is energized (or a higher potential is applied), due to a large current passing through, the second cathode is in a stage of intense reaction at this time, and a relatively intense hydrogen evolution side reaction will occur on the surface of the second cathode, competing with the reduction reaction of Cu ions on the surface of the second cathode. When the second cathode is de-energized (or at a lower potential), it will promote the diffusion of H + near the cathode into the solution, inhibiting the excessive hydrogen evolution side reaction on the surface of the second cathode, promoting the reaction of reducing Cu on the surface of the second cathode, and enhancing the ability of the second cathode to recover Cu.

[0080] In one embodiment of the present invention, the anode is a titanium ruthenium iridium mesh. The anode can also be other dimensionally stable anodes.

[0081] In one embodiment of the present invention, the reference electrode is an Ag / AgCl electrode.

[0082] In one embodiment of the present invention, the first cathode, the second cathode, and the anode are arranged parallel to each other.

[0083] In one embodiment of the present invention, the heavy metal complexes include Cu-EDTA, copper-citric acid, copper ammonia complex, copper cyanide complex, Ni-EDTA, nickel ammonia complex, etc.

[0084] The concentration of the heavy metal complex in the wastewater containing the heavy metal complex is not limited, and can specifically be 0.1 - several thousand mg / L.

[0085] In the embodiments of the present invention, in the reaction method for removing heavy metal complexes and directionally recovering heavy metals in wastewater by pulse voltage, for wastewater containing a high concentration of heavy metal complexes, the first cathode pulse voltage method can be used to strengthen the in-situ generation of hydrogen peroxide and the breaking of the complex.

[0086] In addition, the method of the present invention can also treat wastewater containing ionic heavy metals, and the second cathode pulse voltage method can be used to strengthen the directional recovery of copper ions in the wastewater to the second cathode.

[0087] The present invention will be described in detail below with reference to the embodiments.

[0088] Example 1

[0089] In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A square wave pulse voltage is applied to the CA cathode through an electrochemical workstation (see Figure 2 ), the voltage is set to 0 to -0.9 V, the pulse width is 5 s, and the duty cycle is 100%. A constant potential of -1.35 V is applied to the Ti cathode.

[0090] Using the double-cathode electrochemical system to set the above pulse voltage, with a reaction time of 3 hours, the H2O2 production reaches 22.56 mg / L. The removal rate of the Cu-EDTA complex by this device is 88.14%, and the ratio of Cu recovered by the Ti cathode and the CA cathode is 8.11:1.

[0091] Example 2

[0092] In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A square wave pulse voltage is applied to the CA cathode through an electrochemical workstation (see Figure 3 ), the voltage is set to 0 to -0.9 V, the pulse width is 5 s, and the duty cycle is 150%. A constant potential of -1.35 V is applied to the Ti cathode.

[0093] Using the double-cathode electrochemical system to set the above pulse conditions, with a reaction time of 3 hours, the H2O2 production reaches 16.22 mg / L, the removal rate of the Cu-EDTA complex reaches 80.75%, and the ratio of Cu recovered by the Ti cathode and the CA cathode is 4.97:1.

[0094] Example 3

[0095] In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A triangular pulse voltage is applied to the CA cathode through an electrochemical workstation (see Figure 4 ), the voltage is set to -0.6 to -0.9 V, and the pulse width is 10 s. A constant potential of -1.35 V is applied to the Ti cathode.

[0096] The above pulse voltage was set using a dual-cathode electrochemical system. The reaction time was 3 hours, and the H2O2 production reached 16.61 mg / L. The removal rate of the Cu-EDTA complex by this device was 82.95%, and the ratio of Cu recovery by the Ti cathode to that by the CA cathode was 7.52.

[0097] Example 4

[0098] In the electrochemical reactor, cathode 1 was a CA electrode, cathode 2 was a Ti electrode, the anode was a titanium ruthenium iridium mesh, the reference electrode was Ag / AgCl, and the inter-electrode distance between adjacent electrodes was 1 cm. The concentration of Cu-EDTA in the wastewater was 712.5 mg / L. A differential pulse voltage was applied to the CA cathode through an electrochemical workstation (see Figure 5 ), the starting potential and the ending potential of the voltage were set to -0.6 to -0.9 V, the forward pulse width was 5 s, and the corresponding differential potential was 1.66 mV. A constant potential of -1.35 V was applied to the Ti cathode.

[0099] The above pulse voltage was set using a dual-cathode electrochemical system. The reaction time was 3 hours, and the H2O2 production reached 18.21 mg / L. The removal rate of the Cu-EDTA complex by this device was 83.26%, and the ratio of Cu recovery by the Ti cathode to that by the CA cathode was 5.59.

[0100] Example 5

[0101] In the electrochemical reactor, cathode 1 was a CA electrode, cathode 2 was a Ti electrode, the anode was a titanium ruthenium iridium mesh, the reference electrode was Ag / AgCl, and the inter-electrode distance between adjacent electrodes was 1 cm. The concentration of Cu-EDTA in the wastewater was 712.5 mg / L. A square wave pulse voltage was applied to the Ti cathode through an electrochemical workstation, the voltage was set to 0 to -1.35 V, the pulse width was 5 s, and the duty cycle was 100%. A constant potential of -0.90 V was applied to the CA cathode.

[0102] The above pulse voltage was set using a dual-cathode electrochemical system. The reaction time was 3 hours, the H2O2 production reached 13.21 mg / L, the removal rate of the Cu-EDTA complex was 80.83%, and the ratio of Cu recovery by the Ti cathode to that by the CA cathode was 7.41.

[0103] Example 6

[0104] In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A square wave pulse voltage is applied to the Ti cathode through an electrochemical workstation, the voltage is set to 0~ -1.35 V, the pulse width is 5 s, and the duty cycle is 150%. A constant potential of -0.90 V is applied to the CA cathode.

[0105] Using a dual-cathode electrochemical system to set the above pulse conditions, with a reaction time of 3 hours, the H2O2 production reaches 13.06 mg / L, the removal rate of the Cu-EDTA complex reaches 69.94%, and the ratio of Cu recovery by the Ti cathode and the CA cathode is 7.51:1.

[0106] Example 7

[0107] In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A triangular pulse voltage is applied to the Ti cathode through an electrochemical workstation, the starting potential and the ending potential of the voltage are set to -1.05~ -1.35 V, and the pulse width is 10 s. A constant potential of -0.9 V is applied to the CA cathode.

[0108] Using a dual-cathode electrochemical system to set the above pulse voltage, with a reaction time of 3 hours, the H2O2 production reaches 11.86 mg / L. The removal rate of the Cu-EDTA complex by this device is 78.33%, and the ratio of Cu recovery by the Ti cathode and the CA cathode is 8.19:1.

[0109] Example 8

[0110] In the electrochemical reactor, with the CA cathode as working electrode 1, the Ti sheet as working electrode 2, Ag / AgCl as the reference electrode, and the titanium ruthenium iridium mesh electrode as the anode, the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A differential pulse voltage is applied to the Ti cathode through an electrochemical workstation, the voltage is set to -1.05~ -1.35 V, the pulse width is 10 s, and a constant potential of -0.9 V is applied to the CA cathode.

[0111] Using a dual-cathode electrochemical system to set the above pulse conditions to remove the Cu-EDTA complex in the wastewater, with a reaction time of 3 hours, the H2O2 production reaches 12.03 mg / L, the removal rate of the Cu-EDTA complex reaches 81.67%, and the ratio of Cu recovery by the Ti cathode and the CA cathode is 5.72.

[0112] It can be seen from Examples 1-8 that by applying different pulse modes on the CA cathode, the in-situ generation of H2O2 can be enhanced, thereby improving the efficiency of breaking the complex and degrading heavy metal complexes, and at the same time enhancing the directional recovery efficiency of Cu released by the Ti cathode. 2+ By applying different pulse voltages on the Ti cathode, the disturbance of the electrode liquid interface at the Ti cathode can be enhanced, promoting the diffusion and mass transfer of Cu 2+ , and at the same time enabling H + to quickly diffuse from the cathode surface into the electrolyte solution, inhibiting the hydrogen evolution side reaction on the electrode surface, providing more active sites for the reduction and deposition of free heavy metal ions in the solution on the cathode surface, and further increasing the proportion of heavy metals directionally recovered by the Ti cathode.

[0113] Comprehensively analyzing, among the above different pulse methods, applying a square wave pulse voltage on the CA cathode has the most significant effect on increasing the yield of H2O2, while applying a triangular pulse voltage on the Ti cathode has the best effect on the directional recovery of Cu in the dual-cathode system.

[0114] Comparative Example 1

[0115] A constant potential is applied to both cathodes. In the electrochemical reactor, Cathode 1 is a CA electrode, Cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the electrode spacing between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A constant voltage is applied to the CA cathode and the Ti cathode through an electrochemical workstation.

[0116] Among them, the constant potential applied to the CA cathode is -0.9 V, the potential applied to the Ti cathode is -1.35 V, the yield of H2O2 reaches 12.44 mg / L, the reaction time is 3 hours, and the removal rate of Cu-EDTA is 60%. The ratio of Cu recovered by the Ti cathode and the CA cathode in the obtained chemical reaction device is 4:1.

[0117] Comparative Example 2

[0118] Both cathodes provide pulsed voltages. In the electrochemical reactor, cathode 1 is a CA electrode, cathode 2 is a Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the inter-electrode distance between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A square wave pulsed voltage is applied to the CA cathode through an electrochemical workstation, with the voltage set at 0 to -0.9 V and the pulse width at 10 s. A triangular pulsed voltage is applied to the Ti cathode, with the voltage set at -1.05 to -1.35 V and the pulse width at 10 s. With the above pulsed conditions set in the dual-cathode electrochemical system, the reaction time is 3 hours, the H2O2 production is 11.56 mg / L, the removal rate of the Cu-EDTA complex reaches 65.86%, and the ratio of Cu recovered by the Ti cathode and the CA cathode is 5.73:1.

[0119] When the two cathodes are pulsed simultaneously, it will cause interference between them, making the diffusion direction of Cu ions in the solution disordered and resulting in the inability to be directionally recovered to the Ti cathode. At the same time, the dissolved oxygen in the solution cannot fully diffuse to the surface of the CA cathode during the simultaneous pulse. Therefore, when the two cathodes are pulsed simultaneously, the H2O2 production rate and the directional recovery effect will be poor.

[0120] Comparative Example 3

[0121] In the electrochemical reactor, the cathode is a single CA electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the inter-electrode distance between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A constant voltage is applied to the CA cathode through an electrochemical workstation, with the voltage set at -0.9 V. The reaction time is 3 hours, and the H2O2 production reaches 10.55 mg / L. The removal rate of the Cu-EDTA complex by this device is 50.26%.

[0122] Comparative Example 4

[0123] In the electrochemical reactor, the cathode is a single Ti electrode, the anode is a titanium ruthenium iridium mesh, the reference electrode is Ag / AgCl, and the inter-electrode distance between adjacent electrodes is 1 cm. The concentration of wastewater Cu-EDTA is 712.5 mg / L. A constant voltage is applied to the Ti cathode through an electrochemical workstation, with the voltage set at -1.35 V. The reaction time is 3 hours, and the H2O2 production reaches 1.05 mg / L. The removal rate of the Cu-EDTA complex by this device is 19.13%.

[0124] Test Example 1 Unit energy consumption test of Cu-EDTA degradation in the dual-cathode system under pulsed voltage mode and constant potential

[0125] In Comparative Example 1, when a constant potential was applied to the dual-cathode system, the unit energy consumption required for Cu-EDTA complex breaking was 0.052 KWh / g.

[0126] In Example 1, when a square-wave pulse voltage with a pulse width of 5 s was applied to the CA cathode, the energy consumption of the dual-cathode system was 0.021 KWh / g, which was 59.61% lower than that under the constant potential condition.

[0127] In Example 7, when a triangular pulse voltage with a pulse width of 10 s was applied to the Ti cathode, the energy consumption of the dual-cathode system was 0.033 KWh / g, which was 36.54% lower than that under the constant potential.

[0128] The results show that both of the two optimized cathode pulse voltage modes can effectively reduce the unit energy consumption of Cu-EDTA degradation in the dual-cathode system.

[0129] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A reaction method for enhancing the removal of heavy metal complexes and the directional recovery of heavy metals in wastewater by pulsed voltage, characterized in that It includes the following steps: The reaction method uses two electrochemical workstations and a reactor containing a first cathode, a second cathode, an anode, and a reference electrode. When one electrochemical workstation provides a pulsed voltage to the first cathode or the second cathode, the other electrochemical workstation provides a constant voltage to the remaining cathode. The first cathode is carbon aerogel, carbon fiber, or carbon felt; the second cathode is a titanium plate or stainless steel; the anode is a titanium ruthenium iridium mesh. The pulsed voltage includes a square wave pulsed voltage, a triangular pulsed voltage, or a differential pulsed voltage; the range of the pulsed voltage is: 0 to -2.0 V. In the constant voltage, the constant voltage of the first cathode is -0.6 to -1.5 V, and the constant voltage of the second cathode is -0.8 to -2.0 V. During the reaction process, air or oxygen is continuously introduced into the reaction solution in the reactor. The heavy metal complex includes at least one of Cu-EDTA, copper-citric acid, copper ammonia complex, and copper cyanide complex.

2. The reaction method according to claim 1, wherein The first cathode is carbon aerogel.

3. The reaction method according to claim 1, wherein The second cathode is a titanium plate.

4. The reaction method according to claim 1, wherein The range of the pulsed voltage of the first cathode is 0 to -1.5 V, and the range of the pulsed voltage of the second cathode is 0 to -2.0 V.

5. The reaction method according to claim 4, wherein On the first cathode, the voltage range of the square wave pulse is 0 to -0.9 V, the voltage range of the triangular pulse is -0.6 to -0.9 V, and the voltage range of the differential pulse is -0.6 to -0.9 V; On the second cathode, the voltage range of the square wave pulse is 0 to -1.35 V, the voltage range of the triangular pulse is -1.05 to -1.35 V, and the voltage range of the differential pulse is -1.05 to -1.35 V.

6. The reaction method according to claim 1, wherein The duty cycle of the square wave pulsed voltage is 0 - 300%.

7. The reaction method according to claim 6, wherein The duty cycle of the square wave pulsed voltage on the first cathode is 100%, and the duty cycle of the square wave pulsed voltage on the second cathode is 100%.

8. The reaction method according to claim 1, wherein The pulse width of the pulsed voltage is 0 to 60 s.

9. The reaction method according to claim 8, wherein The pulse width of the first cathode is 2.5 to 10 s, and the pulse width of the second cathode is 5 to 15 s.

10. The reaction method according to claim 1, wherein In the constant voltage, the constant potential of the first cathode is -0.90 V; the constant potential of the second cathode is -1.35 V.

11. The reaction method according to claim 1, wherein The reference electrode is an Ag / AgCl electrode.

12. The reaction method according to claim 1, wherein The first cathode, the second cathode, and the anode are arranged parallel to each other.

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