Method for recovering complexed zinc from wastewater and resource utilization

Abstract

This invention discloses a method for recovering and utilizing complexed heavy metal zinc from wastewater. Under light irradiation, a photocatalyst catalyzes water molecules to generate hydroxyl radicals, which attack the zinc-organic ligand bonds, causing the complexed zinc to dissociate. Simultaneously, the released Zn(II) ions are deposited in situ on a conductive support as elemental zinc under a certain current. This invention achieves free radical dissociation of complexed heavy metal zinc and electrochemical deposition of the dissociated zinc ions without the addition of oxygen or hydrogen peroxide or other oxidants. Furthermore, the photocatalyst can guide uniform zinc deposition. The recovered zinc can be used as the negative electrode in zinc-ion batteries. The photocatalyst also inhibits zinc dendrite growth and hydrogen evolution reaction, thus exhibiting excellent electrochemical performance. In addition, the method of this invention is highly efficient, low-energy, and produces no secondary pollution, making it of significant practical importance for the effective recovery and value-added utilization of complexed heavy metal zinc.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology and resource utilization, specifically to a method for recovering and utilizing complexed heavy metal zinc from wastewater. Background Technology

[0002] With industrial progress and social development, heavy metal pollution has become a major concern and a difficult issue. Heavy metal wastewater mainly contains elements such as copper, nickel, and zinc. The metal ions in these wastewater easily complex with organic ligands in the wastewater, forming metal complexes that are more difficult to degrade and remove. These complexes are chemically stable, greatly increasing the difficulty of removal and posing a serious threat to human health and the ecological environment. Furthermore, there are many types of complexing agents, such as ethylenediaminetetraacetic acid (EDTA) and sodium hexametaphosphate. The sources of heavy metal wastewater are closely related to people's lives, and treating this type of wastewater is one of the key focuses of environmental protection work. Traditional methods such as precipitation and adsorption cannot break the bonds between heavy metal ions and organic ligands, nor can they recover and utilize the released heavy metal ions. Therefore, to achieve sustainable development, it is urgent to develop a new method for treating complexed heavy metal wastewater, simultaneously achieving metal-organic ligand decomposition and metal recovery and resource utilization. Advanced oxidation technologies are effective for degrading heavy metal complex wastewater, but this technology requires the addition of large amounts of strong oxidants and other additives, introducing secondary pollution.

[0003] Photocatalysis refers to physicochemical reactions involving light and is a widely studied technology in recent years. Photocatalysis utilizes solar energy, which is environmentally friendly, economical, efficient, energy-saving, and inexhaustible, meeting current development needs. Therefore, photocatalysis technology can play a role in multiple fields and has the potential for long-term development. Titanium dioxide (TiO2), zinc oxide, tin oxide, and zirconium dioxide are typical metal-based semiconductor materials and were among the earliest semiconductor photocatalysts applied in the field of photocatalysis. They exhibit excellent photocatalytic performance and show significant advantages in degrading organic pollutants, making them relatively ideal photocatalysts. Developing new methods for treating complexed heavy metal wastewater based on photocatalysis technology, while simultaneously achieving decomplexing of organometallic ligands and resource recovery of heavy metals, is of great significance. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a novel method for treating complexed heavy metal zinc in wastewater. By combining photocatalysis and electrochemical technology, the complexed zinc is effectively broken down, and the released Zn(II) is reduced to metallic zinc and uniformly deposited on the surface of a conductive carrier, which then serves as the negative electrode of a zinc-ion battery to achieve resource utilization.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution:

[0006] A method for recovering zinc, a complexed heavy metal, from wastewater includes the following steps:

[0007] (1) A working electrode is prepared by loading a photocatalyst onto a porous conductive support;

[0008] (2) Add the complexed heavy metal zinc wastewater to be treated into a transparent electrolytic cell, use the working electrode obtained in step (1) as the cathode, apply a certain current while irradiating light, and recycle the complexed heavy metal zinc wastewater.

[0009] (3) After the process is completed, the cathode is cleaned and dried to obtain the Zn electrode.

[0010] Further, the photocatalyst mentioned in step (1) is one or a mixture of several of titanium dioxide, zinc oxide, tin oxide, zirconium dioxide, and metal-organic framework materials.

[0011] Further, the porous conductive carrier mentioned in step (1) is at least one of carbon paper, carbon cloth, graphite felt, nickel foam and stainless steel mesh.

[0012] Furthermore, the porous conductive carrier described in step (1) is first soaked in an acid solution for 1-24 hours for hydrophilic treatment before use, and the surface oxide layer and impurities are removed.

[0013] Further, the method for preparing the working electrode in step (1) is as follows: growing the photocatalyst in situ on the porous conductive support, or uniformly coating the photocatalyst on the porous conductive support.

[0014] Furthermore, in step (2), the wavelength of the light used for illumination is 220-388nm.

[0015] Furthermore, in step (2), the current density is 0.1-50 mA / cm². -2 .

[0016] In this invention, the complexed zinc wastewater Zn(II)-EDTA generally originates from wastewater discharged from the electroplating industry, and the concentration range of Zn(II)-EDTA in the wastewater is 10. -4 ~10 2 mg L -1 .

[0017] The beneficial effects of this invention are reflected in:

[0018] This invention utilizes a photocatalytic-electrochemical combined system to generate hydroxyl radicals through photocatalysis without the addition of oxidants such as oxygen or hydrogen peroxide. These hydroxyl radicals attack zinc-organic ligand bonds, causing the complexed zinc to disintegrate. Simultaneously, the released Zn(II) ions are deposited in situ as elemental zinc on a conductive support under a specific current, achieving both radical disintegration of the complexed heavy metal zinc and electrochemical deposition of the disintegrated zinc ions. Furthermore, the selected photocatalyst not only catalyzes the generation of free radicals from water molecules, guiding uniform zinc deposition so that the recovered zinc can be used as the negative electrode in a zinc-ion battery, but also inhibits the nucleation and growth of zinc dendrites and the hydrogen evolution reaction, resulting in excellent electrochemical performance and cycle stability. This invention overcomes the problems of complex processes, large reagent dosages, large sludge production, high energy consumption, and severe secondary pollution associated with traditional heavy metal complex wastewater treatment, achieving effective removal of heavy metal zinc complexes, enrichment and recovery of heavy metal zinc ions, and value-added utilization. Furthermore, the method described in this invention is highly efficient, low in energy consumption, and free from secondary pollution, and has significant practical implications for the recovery, resource utilization, and added-value-added application of complexed heavy metal zinc. Attached Figure Description

[0019] Figure 1 The X-ray diffraction patterns of the titanium dioxide / carbon paper (TiO2 / CP) electrode before and after the reaction in Example 1 are shown.

[0020] Figure 2 The graph shows the removal effect of heavy metal complex Zn(II)-EDTA under different pH conditions in Example 1 and Comparative Examples 1-4.

[0021] Figure 3 The graph shows the effect of different reaction times on the removal of heavy metal ions Zn(II) in Example 2.

[0022] Figure 4 The coin cell symmetric battery assembled with TiO2 / CP@Zn in Example 3 was tested at 2 mA / cm². -2 Current density, 1mAh cm -2 Cyclic performance curves at capacity density. Detailed Implementation

[0023] The present invention will be described in detail below through embodiments, and the features and advantages of the present invention will become clearer and more explicit with these descriptions. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] 1. Preparation of simulated heavy metal complex Zn(II)-EDTA solution:

[0026] 5.7268 g of disodium ethylenediaminetetraacetate (EDTA) was completely dissolved in 1 L of ultrapure water; 2.0923 g of zinc chloride was also completely dissolved in 1 L of ultrapure water. The solutions were mixed at a molar ratio of 1:1 and allowed to stand for 48 hours. The pH of the solution was then adjusted to pH 7, yielding a Zn(II)-EDTA concentration of 1000 mg / L. -1 Simulated wastewater. Diluted to 50 mg / L for degradation experiments. -1 .

[0027] 2. Electrode preparation:

[0028] The carbon paper is first soaked in a mixed acid solution (containing 10% nitric acid and 10% sulfuric acid) for 24 hours for hydrophilic treatment. Titanium dioxide and polyvinylidene fluoride are mixed at a mass ratio of 9:1, and N-methylpyrrolidone is added and thoroughly ground to form a slurry. This slurry is then uniformly coated onto the carbon paper and dried in a vacuum drying oven at 60°C for 12 hours to obtain the TiO2 / CP electrode. The iron sheet is first soaked in detergent to remove residual grease from its surface, then soaked in 1%–2% dilute hydrochloric acid to remove the oxide layer. Finally, it is rinsed with deionized water and dried for later use.

[0029] 3. Degradation experiment process:

[0030] The degradation experiment was conducted in a 100 mL beaker, with a degradation volume of 50 mL. 50 mg L was added to the beaker. -1 The simulated wastewater used was 1 mol L. -1 The pH was adjusted to 4.62 using NaOH and HCl solutions. The prepared TiO2 / CP electrode was used as the working electrode, and the iron electrode as the counter electrode. The electrode was placed in a beaker and connected to an AutoLab electrochemical workstation. The system was operated under illumination (UV-Vis light source provided by a 300W xenon lamp) and a 0.6 mA cm⁻¹ light source. -2 Degradation experiments were conducted under constant current. Samples were taken every 20 minutes and filtered through a 0.22 μm filter membrane. The concentrations of EDTA and zinc ions were measured using a UV-Vis spectrophotometer. After a certain reaction time, the titanium dioxide / carbon paper electrode was removed, washed with ultrapure water, and dried to obtain a zinc anode, TiO2 / CP@Zn. Its X-ray diffraction analysis is as follows: Figure 1 As shown.

[0031] Comparative Example 1

[0032] The experimental method for this comparative example is the same as that for Example 1, except that the pH of the reaction solution prepared during the degradation experiment is adjusted to 8.

[0033] Comparative Example 2

[0034] The experimental method for this comparative example is the same as that for Example 1, except that the pH of the reaction solution prepared during the degradation experiment is adjusted to 6.

[0035] Comparative Example 3

[0036] The experimental method for this comparative example is the same as that for Example 1, except that the pH of the reaction solution prepared during the degradation experiment is adjusted to 4.

[0037] Comparative Example 4

[0038] The experimental method for this comparative example is the same as that for Example 1, except that the pH of the reaction solution prepared during the degradation experiment is adjusted to 2.

[0039] The removal efficiency of the heavy metal complex Zn(II)-EDTA in the above embodiments and comparative examples is shown in the following figures. Figure 2 As shown, the method of this invention can effectively degrade Zn(II)-EDTA heavy metal complexes. After 300 minutes of reaction, Zn(II)-EDTA was degraded by 92%, 87%, 64%, 52%, and 75% at pH 2.0, 4.0, 6.0, 8.0, and 4.62, respectively, indicating that Zn(II)-EDTA is more easily degraded and removed under acidic conditions. The difference in degradation effect is related to the Zn(II)-EDTA degradation at different pH conditions. 2+ The state of EDTA is relevant; Zn(II)-EDTA undergoes protonation at pH 2, existing as Zn-HEDTA- and Zn-H2EDTA. At pH values ​​between 6 and 9, ZnEDTA... 2- It dominates. Protonated zinc complexes are more easily oxidized by active substances than deprotonated zinc complexes, so Zn(II)-EDTA is more easily degraded and removed under acidic conditions.

[0040] Example 2

[0041] Heavy metal ion recovery experiment: The experimental method in this embodiment is the same as in Example 1, except that actual zinc wastewater containing Zn(II)-EDTA is used, and the degradation experiment time is extended to 6 hours. After the experiment, the Zn(II) content in the solution is detected to determine the zinc recovery rate. The calculation method is: R = (C0 - C) / C0 × 100%, where C0 and C represent the initial concentration of Zn(II) and the remaining concentration of Zn(II) at time t, respectively. The relationship between degradation experiment time and zinc recovery rate is as follows: Figure 3 As shown.

[0042] Depend on Figure 2 and Figure 3As can be seen, the Zn(II) ions, after being decomplexed, are reduced and electrodeposited onto the cathode under the influence of current, resulting in a gradual decrease in the Zn(II) ion content in the reaction solution over time. The method of this invention achieves effective removal and recovery of Zn(II)-EDTA heavy metal complexes, and exhibits stable performance.

[0043] Example 3

[0044] The negative electrode, after being degraded for 120 minutes according to the method in Example 2, was taken out, washed with ultrapure water, and dried to obtain a zinc negative electrode material TiO2 / CP@Zn.

[0045] Assemble CR2025 coin cells using an air-filled coin cell packaging machine, in the following order: stainless steel negative electrode shell, TiO2 / CP@Zn, separator (glass fiber separator), TiO2 / CP@Zn, gasket, spring contact, and stainless steel positive electrode shell. Use a 2 mol / L electrolyte. -1 A ZnSO4 aqueous solution was used to assemble TiO2 / CP@Zn / / TiO2 / CP@Zn symmetric cells. A commercially available Zn / / Zn symmetric cell was assembled under the same conditions for comparison. The assembled coin cells were allowed to stand at room temperature and atmospheric pressure for at least 12 hours to allow the electrolyte to fully wet the electrodes.

[0046] Charge-discharge tests were performed on symmetrical coin cells assembled from commercially available Zn and TiO2 / CP@Zn, such as... Figure 4 As shown, compared with commercial Zn / / Zn symmetric cells, TiO2 / CP@Zn / / TiO2 / CP@Zn symmetric cells exhibit significantly improved cycle stability, achieving over 200 hours of cycling.

[0047] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering complexed zinc from wastewater, characterized by, Includes the following steps: (1) Before use, the porous conductive carrier is soaked in an acid solution for 1-24 hours to perform hydrophilic treatment and remove the surface oxide layer and impurities; the photocatalyst is grown in situ on the porous conductive carrier, or the photocatalyst is uniformly coated on the porous conductive carrier to obtain the working electrode. (2) the complex heavy metal zinc wastewater to be treated is added into a transparent electrolytic cell, the working electrode obtained in step (1) is used as a cathode, light is used for illumination, and a current is applied at the same time, so that the complex heavy metal zinc wastewater is recycled and treated; the wavelength of the light used for illumination is 220-388 nm; the density of the current is 0.1-50 mA·cm -2 ; (3) After the treatment is completed, the cathode is cleaned and dried to obtain the Zn electrode.

2. The method for recovering complexed zinc from wastewater according to claim 1, characterized by, The photocatalyst mentioned in step (1) is one or a mixture of several of the following: titanium dioxide, zinc oxide, tin oxide, zirconium dioxide, and metal-organic framework materials.

3. The method for recovering complexed heavy metal zinc from wastewater according to claim 1, characterized in that, The porous conductive carrier mentioned in step (1) is at least one of carbon paper, carbon cloth, graphite felt, nickel foam and stainless steel mesh.

4. The resource utilization of a Zn electrode prepared by the recycling method according to any one of claims 1 to 3 as a negative electrode of a zinc-ion battery.

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