Electrochemical method for simultaneously removing CO2 in atmosphere and recovering zinc in electroplating sludge

Abstract

The invention discloses an electrochemical method for simultaneously removing CO2 in the atmosphere and recovering zinc in electroplating sludge, the zinc in the electroplating sludge is recovered in the form of a sodium zincate solution by coupling a CCUS technology with bipolar membrane electrodialysis, and the method is characterized in that the method is formed by coupling the CCUS technology with the bipolar membrane electrodialysis; according to the method, absorption of CO2 and migration of metal ions in electroplating sludge are achieved through bipolar membrane electrodialysis, zinc recovery is achieved after alkaline leaching separation, and the bipolar membrane electrodialysis system is composed of an anode chamber, an electroplating sludge chamber, a salt chamber, an alkali chamber and a cathode chamber in sequence. The five chambers are sequentially separated by a bipolar membrane, a cation exchange membrane, an anion exchange membrane and another bipolar membrane, the anode chamber and the cathode chamber both take a NaCl solution with the concentration of 2-4 g / L as electrolyte, carbon felts are used as an anode and a cathode, and the anode and the cathode are connected with a direct-current power supply through leads. According to the method, CO2 conversion is completed while zinc in the electroplating sludge is recycled, and carbon neutralization and carbon emission reduction are achieved.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry technology, and particularly relates to an electrochemical method for simultaneously removing CO2 from the atmosphere and recovering zinc from electroplating sludge. Background Art

[0002] Electroplating sludge is solid waste generated during the treatment of electroplating wastewater. Due to its large amount of heavy metals and other pollutants, it has the characteristics of being difficult to degrade, unstable in nature, and highly toxic. In addition, some enterprises gather the electroplating wastewater generated by different production lines and treat them together. At this time, the metal element composition in the obtained electroplating sludge is more complex, mainly including metal elements such as nickel, magnesium, and zinc. When it enters the natural environment without treatment or improper treatment, it will cause soil and water pollution. Some metal ions will also accumulate and enrich in organisms through the food chain, posing a potential threat to human health. Therefore, electroplating sludge is listed in the list of Hazardous Wastes in China, No. HW17. In addition, the heavy metals in electroplating sludge are important valuable resources. If the heavy metals in electroplating sludge can be effectively recovered, it can not only reduce environmental pollution, but also generate greater economic benefits.

[0003] Discharging electroplating sludge into the sea was once a commonly used treatment method. However, this method will have a significant impact on the marine environment. Currently, heat treatment technology, physical treatment, and chemical treatment methods are mostly used to harmlessly treat electroplating sludge, striving to minimize the harm of electroplating sludge to the environment.

[0004] The heat treatment technology is a method of exposing electroplating sludge to a high-temperature environment, causing it to change through chemical reactions, thereby achieving harmless treatment. The heat treatment of electroplating sludge is mainly a process of deep oxidation and melting. Through heat treatment, the toxicity of certain highly toxic components in the electroplating sludge can be reduced, and at the same time, the reduction and volume reduction of the electroplating sludge can be achieved, thus achieving the purpose of treatment. The conventional heat treatment of electroplating sludge usually includes two processes. First, the moisture in the electroplating sludge is evaporated by heating to make it a combustible dry solid, thereby reducing the difficulty of subsequent treatment. Second, the dried sludge is exposed to a high-temperature environment to decompose it into gases and solids. However, although the heat treatment technology can effectively reduce the sludge volume, due to the low calorific value of the electroplating sludge and the small amount of combustible components in the sludge, the heat treatment process of the electroplating sludge requires a large amount of energy, and combustible substances need to be added for auxiliary heat treatment, increasing the production equipment and operating costs. In addition, greenhouse gases are generated during the heat treatment process, which has an impact on the environment, and the solids after pyrolysis also need to be properly disposed of. The physical treatment method mainly uses physical solidification to evaporate or discharge the moisture in the sludge to form a solid with a certain strength. The sludge forms a polymer through a physical solidification binder, and the bonding and solidification process is completed by applying energy (such as pressure, heat, etc.). The solidification and stabilization method has low treatment cost and low technical threshold, and is suitable for popularization. Although most of the electroplating sludge produced in China currently adopts physical solidification treatment to make the electroplating sludge into bricks or cement, physical solidification fails to truly achieve the reduction and resource utilization of electroplating sludge, will occupy a large amount of landfill capacity, and the persistence of the solidification effect of electroplating sludge and the potential secondary dissolution risk of heavy metals in the solidified body are also problems that need to be solved urgently. The chemical treatment method is a treatment method that mixes harmful substances in the electroplating sludge with a curing agent or solvent to undergo a chemical reaction to form a water-insoluble compound and produce a stable solid waste. Through the active components in the curing agent or solvent (mainly anions that are easy to combine with metal cations to produce precipitation, such as phosphates, carbonates, sulfides, etc.) reacting with harmful substances such as heavy metal ions in the electroplating sludge to form water-insoluble solid compounds, the harmful substances in the electroplating sludge are solidified and stabilized, and the total amount of harmful substances is reduced, thereby achieving the purpose of reducing and eliminating its harm to the environment. Its advantages include that the cured product has high stability and mechanical strength, can reduce the volume and harm of hazardous waste, and turn waste into useful resources, etc.

[0005] Fossil fuels still dominate the world's energy consumption structure. At the same time, during the use of fossil fuels, a large amount of greenhouse gases are generated, and the emission of greenhouse gases causes the greenhouse effect to intensify, thereby leading to global warming.

[0006] As the main product after the combustion of fossil fuels, compared with other greenhouse gases, the concentration change of CO2 is the most obvious, and it remains in the atmosphere for a longer time.

[0007] In recent years, developed countries have taken CO2 capture and storage technology as the main means of CO2 emission reduction. This technology integrates CO2 capture and storage, and can effectively reduce CO2 emissions. Among them, the post-combustion capture method is suitable for large-scale coal-fired power plants, but it has high costs, great restrictions on storage sites and the risk of CO2 leakage. Now, a new way of CO2 emission reduction has emerged. Through CO2 capture and utilization technology, CO2 end-of-pipe emission reduction is achieved. This method mainly uses calcium- and magnesium-rich ores or alkaline solid wastes (such as metals and their oxides, etc.) in nature to carry out carbonation reactions with the greenhouse gas CO2, and permanently stores CO2 in the form of carbonate mineral products.

[0008] In the CCUS process, dissolving more CO2 into anionic form can promote its reaction with dissolved metals. At present, adding alkali to promote CO2 dissolution is the most commonly used and simplest means. However, due to the excessively high cost of the external alkali source, it always faces the problems of greening and whether economic carbon fixation can be achieved. As a new emerging electrochemical separation technology (disclosed in the literature Journal of Membrane Science, 2008, 325(2): 528-536), the bipolar membrane electrodialysis system has the advantages of simple operation, low energy consumption, no consumption of chemical additives, no by-products, etc., and is regarded as a potential green chemical process. It can synergistically achieve three processes: water dissociation to produce alkali, metal ion migration, and chemical reaction, and is considered an effective tool for producing alkali without generating hydrogen and oxygen. It has been widely used in fields such as chemical desalination, acid-base preparation, and purification and concentration of industrial wastewater. Summary of the Invention

[0009] The purpose of the present invention is to provide an electrochemical method for simultaneously removing CO2 from the atmosphere and recovering zinc from electroplating sludge.

[0010] To achieve the object of the present invention, the technical solution adopted is: an electrochemical method for simultaneously removing CO2 from the atmosphere and recovering zinc from electroplating sludge, which uses CCUS technology to couple with a bipolar membrane electrodialysis system to recover zinc in the water body in the form of sodium zincate solution. The electrochemical method is characterized in that it is composed of the coupling of CCUS technology and a bipolar membrane electrodialysis system. The bipolar membrane electrodialysis system is used to realize the absorption of CO2 and the dissolution and migration processes of metal ions in electroplating sludge, and the recovery of zinc ions is realized after alkali leaching separation. The bipolar membrane electrodialysis system consists of five electrolytic cells, which are an anode chamber, an electroplating sludge chamber, a salt chamber, an alkali chamber, and a cathode chamber in sequence. The five chambers are separated by a bipolar membrane (BPM-1), a cation exchange membrane (CEM), an anion exchange membrane (AEM), and a bipolar membrane (BPM-2) in sequence. The anode chamber and the cathode chamber are both filled with 2-4 g / L NaCl solution as the electrolyte, and carbon felt is used as the anode and the cathode. The anode and the cathode are connected to a DC power supply with wires.

[0011] Preferably, in the electrochemical method, the arrangement order of the membranes from the anode to the cathode end in the zinc-containing electroplating sludge recovery unit is a bipolar membrane (BPM-1), a cation exchange membrane (CEM), an anion exchange membrane (AEM), and a bipolar membrane (BPM-2) in sequence.

[0012] Preferably, in the electrochemical method, zinc in the water body is recovered in the form of sodium zincate solution. CCUS technology is coupled with the bipolar membrane electrodialysis system, and the bipolar membrane electrodialysis system is used to absorb CO2 to generate CO3 2- , and the metal ions (Ni + , Mg 2+ , Zn 2+ ) in the electroplating sludge are dissolved by generating H 2+ and react with CO3 2- to fix CO3 2- . After filtering the solid in the salt chamber and performing alkali leaching separation treatment, the generated sodium zincate solution can be used as the electrolyte in the galvanizing process.

[0013] Preferably, in the electrochemical method, zinc in the water body is recovered in the form of sodium zincate solution, and carbon felt is used as the anode and the cathode.

[0014] Advantages of the present invention: The bipolar membrane electrodialysis system described in the present invention can rapidly dissociate the water molecules in the middle layer of the bipolar membrane under the action of an electric field to generate H + and OH - . The generated OH -Furthermore, it combines with CO2 to form carbonate ions, and then combines with metal ions to form carbonates. Without the addition of an external alkali source, it has gradually been applied in the field of environmental protection. This technology utilizes the advantages of bipolar membrane electrodialysis to separate and enrich ions in a solution. It couples the CCUS technology with a bipolar membrane electrodialysis system. Through the OH - provided by the hydrolysis of the bipolar membrane to absorb CO2, generating CO3 2- which dissolves in the alkali chamber and migrates to the salt chamber under the action of the electric field force through an anion exchange membrane. The zinc-containing electroplating sludge (containing metals such as zinc, magnesium, and nickel) is introduced into the electroplating sludge chamber. In the electroplating sludge chamber, the H + produced by the hydrolysis of the bipolar membrane dissolves the metal ions (Ni 2+ , Mg 2+ , Zn 2+ ) in the electroplating sludge. At the same time, under the action of the electric field force, the metal ions migrate to the salt chamber through a cation exchange membrane. The Ni 2+ , Mg 2+ , Zn 2+ in the salt chamber reacts with CO3 2- to produce the corresponding carbonates (nickel carbonate, magnesium carbonate, zinc carbonate). After filtration, the solid is subjected to alkali leaching separation treatment, and the resulting sodium zincate solution can be used as the electrolyte in the zinc plating process. In the prior art, the electroplating sludge is converted into a catalyst for the electrocatalytic reduction of CO2 by high-temperature pyrolysis, and then the conversion of CO2 is achieved through the electroreduction process as a means of co-treating electroplating sludge and CO2. However, such methods require the treatment of electroplating sludge at high temperatures, with high energy consumption and low electrocatalytic reduction efficiency, resulting in low CO2 conversion rate. The method shown in the present invention, which couples the CCUS technology with a bipolar membrane electrodialysis system, does not need to operate at high temperatures. While recovering zinc from electroplating sludge under milder conditions, the CO2 conversion rate is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of the principle of the CCUS technology coupled with a bipolar membrane electrodialysis system of the present invention for recovering zinc in water in the form of sodium zincate solution; in the figure, BPM: bipolar membrane, CEM: cation exchange membrane, AEM: anion exchange membrane.

[0016] Figure 2 is the recovery rate of Zn 2+ in electroplating sludge under different current density conditions of the present invention.

[0017] Figure 3 is the recovery rate of Mg 2+ in electroplating sludge under different current density conditions of the present invention.

[0018] Figure 4 is the recovery rate of Ni in electroplating sludge under different current density conditions of the present invention.2+ Recovery rate. Detailed implementation mode

[0019] In order to make the technical problems, technical solutions and effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments and drawings.

[0020] The present invention provides an electrochemical method for recovering zinc from electroplating sludge: the principle of the CCUS technology coupled with a bipolar membrane electrodialysis system for recovering zinc in the water body in the form of sodium zincate solution (see Figure 1 ) is as follows: using carbon felt as the anode and cathode, the electrode chambers of the anode and cathode are both filled with 2 - 4 g / L NaCl solution as the electrolyte, five electrolytic cells are made of plexiglass, and the structure of the electrolytic cell is an anode chamber, an electroplating sludge chamber, a salt chamber, an alkali chamber, and a cathode chamber. The five chambers are separated by a bipolar membrane (BPM - 1), a cation exchange membrane (CEM), an anion exchange membrane (AEM), and a bipolar membrane (BPM - 2) in sequence (Journal of Membrane Science, 2008, 325(2): 528 - 536). The bipolar membrane is a special ion exchange membrane, which is a composite anion and cation membrane made of a cation membrane and an anion membrane. The embodiments of the present invention use conventional commercially available products; when the bipolar membrane electrodialysis system works, carbon felt is used as the anode and cathode, and the anode and cathode are connected to a DC power supply with wires. After the DC power supply is energized, under the action of the electric field force, the H + migrates to the electroplating sludge chamber and undergoes an ion exchange reaction with the metals in the electroplating sludge, and transfers metal ions (Ni 2+ , Mg 2+ , Zn 2+ , etc.) into the solution. At the same time, the OH - generated by BPM - 2 migrates to the alkali chamber under the action of the electric field force, and CO2 is introduced into the alkali chamber through a conduit. In the closed alkali chamber, OH - continuously absorbs CO2 through equations 1 and 2 and generates CO3 2- . In addition, under the action of the electric field force, the metal ions in the electroplating sludge chamber migrate to the salt chamber through the CEM, and the CO3 2- in the alkali chamber migrates to the salt chamber through the AEM. The metal components in the zinc - containing electroplating sludge react with CO3 2-Reactions occur to form corresponding carbonate precipitates (nickel carbonate, magnesium carbonate, zinc carbonate). The carbonate precipitates obtained in the salt chamber are filtered out. NaOH solution is added to the filtered carbonates for alkali leaching separation. In this process, zinc carbonate reacts chemically with NaOH and dissolves in the NaOH solution in the form of sodium zincate (Equation 3), while nickel carbonate and magnesium carbonate react with NaOH to form more stable Ni(OH)2 and Mg(OH)2 (Equations 4 and 5). Through filtration, the separation of Ni(OH)2 and Mg(OH)2 and the recovery of the sodium zincate solution can be achieved.

[0021] OH - + CO2 → HCO3 - (1)

[0022] HCO3 - + OH - → CO3 2- (2)

[0023] ZnCO3 + 4NaOH → Na2ZnO2 + Na2CO3 + 2H2O (3)

[0024] NiCO3 + 2NaOH →Ni(OH)2↓ + Na2CO3 (4)

[0025] MgCO3 + 2NaOH →Mg(OH)2↓ + Na2CO3 (5) Specific examples:

[0027] Sludge: The electroplating sludge is taken from a certain electroplating factory in Zhangpu, Fujian. The contents of Zn 2+ , Mg 2+ , Ni 2+ in the electroplating sludge are 127 g / kg, 3.6 g / kg, and 10.5 g / kg respectively.

[0028] Experimental conditions: Using Figure 1 the device as the experimental device for this example, using carbon felt as the anode and cathode. The anode and cathode are connected to a DC power supply with wires. After the DC power supply is energized, the currents of bipolar membrane electrodialysis are 0.24, 0.36, 0.48, 0.60, and 0.72 A respectively, and the corresponding current densities are 20, 30, 40, 50, and 60 mA / cm 2; 5 g of electroplating sludge and 50 mL of carbon dioxide-free distilled water were placed in the electroplating sludge chamber. During the experiment, a mechanical stirrer was used to stir the electroplating sludge in the electroplating sludge chamber at a stirring rate of 150 rpm; the metal ion content in the salt chamber was measured every 1 h; at normal temperature and pressure, the rate of CO2 input into the alkali chamber was 6 L / h. The carbonate precipitate obtained in the salt chamber was filtered out, and NaOH solution was added to the filtered carbonate for alkali leaching separation. The specific alkali leaching process was as follows: The precipitate mixture (carbonate) was added to 2 mol / L NaOH solution, and a constant temperature water bath was carried out at 70 - 80 °C. While the water bath was ongoing, the solution was continuously stirred (stirring rate was 200 rpm) for 1 h. After 1 h, the insoluble substances were filtered. Through filtration, the separation of Ni(OH)2 and Mg(OH)2 and the recovery of sodium zincate solution were achieved, and sodium zincate solution was obtained.

[0029] Experimental results:

[0030] 1) When the current densities were 20, 30, 40, 50, and 60 mA / cm 2 respectively, after 10 hours, the recovery rates of Zn 2+ in the salt chamber were 78.7%, 82.5%, 89.4%, 94.1%, and 98.4% (as Figure 2 shown), and the Zn 2+ concentrations in the salt chamber were 11.1 g / L, 11.6 g / L, 12.6 g / L, 13.3 g / L, and 13.9 g / L; the recovery rates of Mg 2+ were 55.5%, 61.6%, 64.7%, 66.3%, and 72.9% (as Figure 3 shown), and the corresponding Mg 2+ concentrations were 0.22 g / L, 0.25 g / L, 0.26 g / L, 0.27 g / L, and 0.29 g / L; the recovery rates of Ni 2+ in the salt chamber were 79.4%, 82.6%, 90.8%, 96.5%, and 99.2% (as Figure 4 shown), and the corresponding Ni 2+ concentrations were 0.93, 0.96, 1.06, 1.13, and 1.16 g / L.

[0031] 2) When the current densities were 20, 30, 40, 50, and 60 mA / cm 2 respectively, after 10 hours, the amounts of CO2 absorbed were 1.78 mol / L, 2.13 mol / L, 2.57 mol / L, 2.94 mol / L, and 3.23 mol / L, and CO3 2-The amounts are 0.22 mol / L, 0.26 mol / L, 0.31 mol / L, 0.35 mol / L, and 0.38 mol / L respectively, and the finally obtained concentrations of sodium zincate are 0.160 mol / L, 0.167 mol / L, 0.181 mol / L, 0.188 mol / L, and 0.199 mol / L respectively.

Claims

1. An electrochemical method for simultaneously removing CO2 from the atmosphere and recovering zinc from electroplating sludge, using CCUS technology coupled with a bipolar membrane electrodialysis system to recover zinc from water in the form of sodium zincate solution, characterized in that The electrochemical method is formed by coupling CCUS technology with a bipolar membrane electrodialysis system. The bipolar membrane electrodialysis system is used to realize the absorption of CO2 and the dissolution and migration of metal ions in electroplating sludge, and the recovery of zinc ions after alkaline leaching separation. The bipolar membrane electrodialysis system is composed of five electrolytic cells, which are respectively an anode chamber, an electroplating sludge chamber, a salt chamber, an alkali chamber, and a cathode chamber. The five chambers are separated by a bipolar membrane (BPM-1), a cation exchange membrane (CEM), an anion exchange membrane (AEM) and a bipolar membrane (BPM-2). The anode chamber and the cathode chamber both use 2-4 g / L NaCl solution as the electrolyte, and carbon felt is used as the anode and cathode. The anode and the cathode are connected to a DC power supply with a wire.

2. The electrochemical method according to claim 1, characterized in that The arrangement order of the zinc-containing electroplating sludge recovery unit from the anode to the cathode end membrane is bipolar membrane (BPM-1), cation exchange membrane (CEM), anion exchange membrane (AEM) and bipolar membrane (BPM-2).

3. The electrochemical method according to claim 1, characterized in that Recover zinc from water in the form of sodium zincate solution, couple CCUS technology with bipolar membrane electrodialysis system, and use bipolar membrane electrodialysis system to absorb CO2 and produce CO3 2- , and by generating H + Dissolve metal ions (Ni 2+ Mg 2+ 、Zn 2+ ) and CO3 2- Reacts to fix CO3 2- The solids in the salt chamber are filtered and then separated by alkaline leaching. The resulting sodium zincate solution can be used as an electrolyte in the zinc plating process.

4. The electrochemical method according to claim 1, characterized in that Zinc in water is recovered in the form of sodium zincate solution, and carbon felt is used as the anode and cathode.

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