A method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complex

Abstract

The present invention relates to a method for efficiently electrochemically reducing and recovering copper from wastewater containing copper complexes, comprising: using a MoS2 / GF electrode as the cathode, a Pt electrode as the anode, separating the anode and cathode chambers with an ion exchange membrane, using wastewater containing an electrolyte and copper complexes to be treated as the electrolyte, and performing an electrochemical reduction reaction to obtain treated wastewater. Compared with the prior art, the present invention prepares a graphite felt electrode loaded with MoS2 by hydrothermally modifying MoS2 on the graphite felt. Using this electrode as the cathode and adopting a constant potential method to treat wastewater containing copper complexes, the removal of copper complexes and the direct recovery of metallic copper on the electrode are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical reduction treatment of hardly biodegradable heavy metal-organic complexes in industrial wastewater, and relates to a method for efficiently electrochemically reducing and recovering copper from wastewater containing copper complexes, and particularly relates to an electrochemical method for efficiently removing and recovering copper from wastewater containing copper complexes realized by a cathode catalyst of MoS 2 -loaded graphite felt. Background Art

[0002] Wastewater containing copper complexes is a typical heavy metal wastewater, mainly derived from industries such as electroplating, smelting, and printed circuit board manufacturing. Heavy metal complexes are highly toxic and persistent, having a profound and difficult-to-recover impact on the environment, and are a challenge in environmental governance. Direct discharge of untreated industrial wastewater containing copper complexes will cause serious environmental pollution and ecological deterioration.

[0003] The main treatment methods for wastewater containing copper complexes include physical methods and chemical methods. Physical methods such as adsorption use adsorbents with a high specific surface area to achieve the enrichment and removal of complexes. Although this method has a relatively low cost, the treatment efficiency is not high, and it is difficult to realize the resource recovery of Cu. Chemical methods achieve the removal of copper-containing pollutants and the synchronous recovery of copper through chemical reactions. The current mainstream chemical treatment technology is to first oxidize and break the complex to release copper ions in the complex, and then precipitate or reduce and recover the free copper ions. However, this method has complex operations, high energy consumption, long time, low efficiency, and is difficult to operate industrially.

[0004] The direct electrochemical reduction method is a relatively promising method, which is more operable than the tandem technology of first oxidizing and breaking the complex and then recovering copper. The electrochemical reduction method has a high spontaneity thermodynamically, but proceeds relatively slowly kinetically. The main reason can be attributed to the stable coordination structure of the Cu complex, resulting in most of the complex molecules being in a non-activated state with a lower energy, so a suitable catalyst is needed to promote the electrochemical reduction rate of the copper complex. Traditional research mainly uses non-active materials such as titanium and carbon as the cathode, and this kind of electrode has two important defects. First, the electrochemical activity of this kind of electrode is low and it cannot efficiently reduce the reactant molecules near the electrode surface. Second, due to the occurrence of the hydrogen evolution side reaction during the reduction process, a lower current efficiency and higher energy consumption are caused. Developing an efficient cathode catalyst is crucial for the treatment of wastewater containing copper complexes. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for efficiently electrochemically reducing and recovering copper from wastewater containing copper complexes.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A wastewater treatment method, comprising:

[0008] Using a MoS 2 / GF electrode as the cathode, Pt as the anode, an ion exchange membrane separating the anode and cathode chambers, and using wastewater containing an electrolyte and a copper complex to be treated as the electrolyte to conduct an electrochemical reduction reaction to obtain treated wastewater.

[0009] Further, in the electrochemical reduction reaction, a saturated calomel electrode is used as the reference electrode, and the cathode potential is -0.65V to -0.75V.

[0010] Further, the copper complex to be treated includes at least one of CuEDTA, copper citrate, or copper diethylenetriaminepentaacetate.

[0011] Further, the electrolyte includes sodium sulfate.

[0012] Further, the preparation method of the MoS 2 / GF electrode includes: mixing a molybdenum source and a sulfur source in a solution to obtain a MoS 2 precursor solution; placing a graphite felt in the MoS 2 precursor solution and conducting a hydrothermal reaction to obtain the MoS 2 / GF electrode.

[0013] Further, the molybdenum source is sodium molybdate, and the sulfur source is thiourea.

[0014] Further, the molar ratio of sodium molybdate to thiourea is 1:(4 - 6).

[0015] Further, in the hydrothermal reaction, the reaction temperature is 180 - 220°C, and the reaction time is 22 - 28h.

[0016] Further, the graphite felt is curled into a column and erected in the MoS 2 precursor solution.

[0017] Further, before the graphite felt is placed in the MoS 2 precursor solution, it is ultrasonically cleaned successively with dichloromethane, hydrochloric acid, ethanol, and water.

[0018] Compared with the prior art, the present invention has the following characteristics:

[0019] 1) By hydrothermally modifying MoS 2 on the graphite felt, a graphite felt electrode loaded with MoS 2 is prepared. Using this electrode as the cathode and adopting the potentiostatic method to treat wastewater containing copper complexes, the removal of copper complexes and the direct recovery of metallic copper on the electrode are realized. The mechanism is as follows:

[0020] First, the copper-containing complex in the solution mass-transfers to the cathode surface driven by the electrochemical potential; then the complex undergoes a complex-breaking process and transforms from the complexed state to free metal ions; finally, the free copper ions gain electrons and are reduced to metal copper particles, while the ligand returns to the solution driven by the electrochemical potential. Due to the strong catalytic effect of MoS 2 , the reduction rate of the copper complex on the cathode surface is higher than that of non-active electrodes such as graphite felt and titanium plate. And due to the strong catalytic effect of MoS 2 on the reduction of CuEDTA, its removal rate is limited by the mass-transfer process. The electrode material prepared by the present invention has good stability and excellent regeneration performance;

[0021] 2) The raw materials for preparing the electrode used in the present invention, namely carbon felt, thiourea and sodium molybdate, are all cheap and easily available, and the preparation method is simple. Therefore, the manufacturing cost of the electrode is relatively low, making it suitable for large-scale applications;

[0022] 3) By first removing the heavy metal ions in the complex, the present invention destroys the molecular structure of the pollutant, improves the BOD 5 / COD, making the wastewater more suitable for subsequent biochemical treatment and facilitating the final up-to-standard discharge of the effluent. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 For comparing the cathode performance of removing CuEDTA in the electrolytic cell in Example 2;

[0024] Figure 2 For the removal rate of CuEDTA by MoS 2 / GF at different cathode potentials in the electrolytic cell in Example 3;

[0025] Figure 3 For the recycling performance of the removal of CuEDTA by MoS 2 / GF in the electrolytic cell in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0027] An electrochemical method for treating copper complex-containing wastewater with MoS 2 -modified graphite felt includes:

[0028] Introduce the wastewater containing the copper complex to be treated and the electrolyte solution into the electrolytic cell. Use MoS 2 / GF electrode as the cathode, Pt as the anode, and separate the anode and cathode chambers with an ion exchange membrane. Perform electrodeposition treatment on the copper complex-containing wastewater by the potentiostatic method, that is, carry out an electrochemical reduction reaction, so as to remove the copper complex and recover metallic copper, and obtain the treated wastewater.

[0029] Among them, the copper complex to be processed includes CuEDTA; the electrolyte used includes sodium sulfate; in the electrochemical reduction reaction, a saturated calomel electrode is used as the reference, and the cathode potential is -0.65V to -0.75V.

[0030] MoS 2 The MoS

[0031] / GF electrode is prepared by a one-step hydrothermal method, including the following steps:

[0032] S1: Cleaning of graphite felt:

[0033] Take the graphite felt and ultrasonically clean it successively with dichloromethane, hydrochloric acid (preferably with a concentration of 1M), ethanol, and water (preferably ultrapure water) to remove the impurities attached to the surface of the graphite felt, and then place it in an oven for drying for later use (the drying temperature is preferably 60°C); 2 S2: Preparation of MoS

[0034] Mix the molybdenum source and sulfur source in water and stir to dissolve them fully to obtain the MoS 2 precursor solution; among them, the molybdenum source is preferably sodium molybdate, and the sulfur source is preferably thiourea; the molar ratio of sodium molybdate to thiourea is preferably 1:(4 - 6);

[0035] S3: Preparation of MoS 2 / GF electrode:

[0036] Transfer the MoS 2 precursor solution to a Teflon hydrothermal kettle, curl the graphite felt into a column and stand it upright in the MoS 2 precursor solution, place the hydrothermal kettle in an oven, and carry out a hydrothermal reaction at 180 - 220°C for 22 - 28h. Take out the prepared electrode material, wash it clean with ultrapure water, and then place it in a vacuum oven for drying to obtain the MoS 2 / GF electrode.

[0037] The active cathode has the advantages of strong catalytic reduction ability for CuEDTA and good selectivity. The mechanism is as follows: First, pollutants such as CuEDTA in the solution, copper-containing complexes, transfer mass to the cathode surface under the drive of the electrochemical potential; then CuEDTA undergoes a complex-breaking process under the catalytic action of MoS 2 and changes from the complex state to free metal ions; finally, the free copper ions gain electrons and are reduced to metal copper particles, and the ligand returns to the solution under the drive of the electrochemical potential. The selectivity of this electrode is relatively strong, and it has a higher selectivity compared to the hydrogen evolution reaction, so the Faraday efficiency is higher and the energy consumption is lower.

[0038] This embodiment is implemented on the premise of the technical solution of the present invention, and gives the detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0039] In the following examples, unless otherwise specified, the Pt sheet is a commercial Pt sheet anode with 99.99% purity, the volumes of both the anode and cathode chambers are 30 mL, the geometric areas of the anode and cathode electrodes are 3 cm 2 , the concentration of sodium sulfate electrolyte is 0.5 M, the concentration of copper complex CuEDTA in the wastewater is 1 mM, the working potential is provided by an electrochemical workstation, and the running time is 10 min.

[0040] Example 1:

[0041] A one-step hydrothermal preparation method of MoS 2 / GF electrode, including the following steps:

[0042] S1: Cleaning of graphite felt:

[0043] Take a 2×6 cm 2 graphite felt and wash it successively with dichloromethane, 1 M hydrochloric acid, ethanol, and ultrapure water, and assist with ultrasonic cleaning to remove impurities attached to the surface of the graphite felt, and then place it in an oven at 60 °C for drying and standby;

[0044] S2: Preparation of MoS 2 precursor solution:

[0045] Weigh 0.21 g of sodium molybdate with an electronic balance, and then weigh 0.38 g of thiourea. Dissolve the two in 30 mL of ultrapure water and stir to make it fully dissolved to obtain MoS 2 precursor solution;

[0046] S3: Preparation of MoS 2 / GF electrode:

[0047] Transfer the MoS 2 precursor solution to a 50 mL Teflon hydrothermal reactor. Roll the graphite felt into a column and stand it upright in the MoS 2 precursor solution. Place the hydrothermal reactor in an oven and carry out a hydrothermal reaction at 200 °C for 24 h. Take out the prepared electrode material, wash it clean with ultrapure water, and then place it in a vacuum oven for drying. Cut the dried electrode material into 2×2 cm 2 small pieces for standby to obtain MoS 2 / GF electrode.

[0048] Example 2: Influence of different electrode materials on Cu removal effect

[0049] This example is used to study the influence of different electrode materials on the Cu removal effect:

[0050] The wastewater containing copper complex is introduced into an electrolytic cell, and the CuEDTA concentration of the wastewater is 1 mM. Using a Pt sheet as the anode, five different electrode materials are selected for the cathode, namely the MoS 2 / GF electrode prepared in Example 1, a Ti plate, a graphite felt, Ni / GF, and Cu / GF. 0.5 M sodium sulfate is used as the electrolyte, and magnetic stirring is carried out in the cathode chamber. The removal experiment of CuEDTA is carried out at the same cathode potential (-0.7 V, relative to the saturated calomel electrode). The results show that under the same cathode potential for 10 min, the results are as Figure 1 shown. It can be seen from the figure that the removal rates of CuEDTA by MoS 2 / GF, Ti plate, graphite felt, Ni / GF, and Cu / GF are 84%, 40%, 10%, 40%, and 10% respectively. This example fully demonstrates that the selected active cathode has higher activity for the reduction and removal of CuEDTA than the traditional inactive cathode.

[0051] Among them, both Ni / GF and Cu / GF are prepared by the dot deposition method.

[0052] Preparation of Ni / GF: Using a cleaned 2×2 cm 2 GF as the working electrode, a Pt sheet of the same size as the counter electrode, and a saturated calomel electrode as the reference electrode. 30 mL of 0.1 M nickel chloride is used as the electrolyte solution, and Ni / GF can be prepared by electro-deposition at -1 V for 300 s.

[0053] Preparation of Cu / GF: Using a cleaned 2×2 cm 2 GF as the working electrode, a Pt sheet of the same size as the counter electrode, and a saturated calomel electrode as the reference electrode. 30 mL of 0.1 M copper chloride is used as the electrolyte solution, and Cu / GF can be prepared by electro-deposition at -0.3 V for 300 s.

[0054] Example 3:

[0055] This example is used to study the influence of different working potentials on the Cu removal effect:

[0056] The difference compared with Example 2 is only that: the cathode potentials are -0.65 V, -0.70 V, and -0.75 V respectively, and the cathode material is the MoS 2 / GF electrode prepared in Example 1; the rest is the same as Example 2.

[0057] The results are as Figure 2 shown. It can be seen from the figure that the reduction and removal rates of CuEDTA by MoS 2 / GF are almost the same, indicating that the CuEDTA reaction in this system is limited by the mass transfer step, and the chemical reaction step has a relatively fast reaction rate due to strong catalytic performance and is in an approximate equilibrium state. This example fully demonstrates the selected MoS2 The electrocatalytic reduction potential of / GF for CuEDTA is extremely high.

[0058] Example 4:

[0059] This example is used to study the cyclic durability of the MoS 2 / GF electrode:

[0060] The difference compared with Example 2 is only that: the same MoS 2 / GF electrode is used to repeat the experiment, and the rest is the same as Example 2.

[0061] The results are as Figure 3 shown. It can be seen from the figure that the reduction removal rate of MoS 2 / GF for CuEDTA decreases with the progress of the cyclic experiment, which is because the electrode surface is gradually covered by inactive metallic Cu. After the third cycle, the electrode is soaked in saturated ethylenediaminetetraacetic acid to recover metallic copper and regenerate the electrode, and the performance of the electrode is completely restored. This example fully demonstrates the stability and high practical application value of the selected MoS 2 / GF in the reduction process of CuEDTA.

[0062] The above description of the embodiments is 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 should be within the protection scope of the present invention.

Claims

1. A method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complexes, characterized in that, the method comprises: Using the MoS 2 / GF electrode as the cathode, Pt as the anode, and an ion exchange membrane to separate the anode and cathode chambers, using wastewater containing an electrolyte and a copper complex as the electrolyte solution, an electrochemical reduction reaction is carried out to obtain the treated wastewater; The described MoS 2 / GF electrode preparation method includes: mixing sodium molybdate and thiourea in a solution at a molar ratio of 1:(4-6) to obtain a MoS 2 precursor solution; curling a graphite felt into a column and standing it upright in the MoS 2 precursor solution, and carrying out a hydrothermal reaction at 180-220°C for 22-28 h to obtain a MoS 2 / GF electrode.

2. The method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complexes according to claim 1, characterized in that, in the electrochemical reduction reaction, a saturated calomel electrode is used as the reference electrode, and the cathode potential is -0.65V to -0.75V.

3. The method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complexes according to claim 1, characterized in that, the copper complex comprises at least one of CuEDTA, copper citrate or copper diethylenetriaminepentaacetate.

4. The method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complexes according to claim 1, characterized in that, the electrolyte comprises sodium sulfate.

5. The method for highly efficient electrochemical reduction and recovery of copper from wastewater containing copper complexes according to claim 1, characterized in that, The described graphite felt is ultrasonically cleaned successively with dichloromethane, hydrochloric acid, ethanol, and water before being placed in the MoS 2 precursor solution.

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