Comprehensive Analysis of Electroplating Heavy Metal Wastewater Treatment Technology Electroplating is a process that uses electrochemical methods to decorate, protect, and obtain certain new properties of metallic and non-metallic surfaces. In order to ensure the quality of electroplating products, the metal coating has a smooth and good appearance and solid with the substrate, must be plated on the surface of the plating before the dirt (oil, rust, oxide, etc.) thoroughly cleaned and plated After plating the surface of the attachment solution to clean. Therefore, the general electroplating process inevitably discharge a large number of electroplating wastewater, electroplating wastewater treatment must be carried out, heavy metal wastewater treatment. Electroplating wastewater treatment is a difficult to completely control and more complex mixed heavy metal wastewater treatment, electroplating wastewater treatment must be based on electroplating wastewater quality, water and electroplating process conditions, production load, operation management and water use and other factors. Electroplating heavy metal wastewater treatment of complex water quality composition is not easy to control, which contains cyanide, acid, alkali, hexavalent chromium, copper, zinc, cadmium, nickel, gold, silver and other heavy metal pollutants, Teratogenic, mutagenic toxic substances, great harm to humans. Electroplating wastewater treatment, mainly for electroplating rinse wastewater, passivation wastewater, acid pickling wastewater plating, brush floor and plate wastewater and due to poor operation or management caused by the "run, run, drip, drain" generated wastewater, the other As well as the discharge of water for personal use in wastewater treatment and drainage of laboratories. Electroplating waste water pollution of the environment there are two main ways, one is the discharge of less concentrated high concentration of electroplating waste, one is the large amount of relatively low concentration of electroplating wastewater (mainly waste water) emissions. The purpose of electroplating waste water treatment is to remove the harmful and toxic substances in the waste water for disposal or recycling, or to make the toxic substances into non-toxic substances. Current status of plating heavy metal wastewater treatment technology Chemical precipitation Chemical precipitation is the process of converting heavy metals that are dissolved in wastewater into water-insoluble heavy metal compounds, including neutralization and precipitation, and sulfide precipitation. Neutralization and precipitation method In the heavy metal-containing wastewater by adding alkali and neutralization reaction, so that the formation of heavy metals in water-insoluble hydroxide precipitation form to be separated. Neutralization precipitation method is simple, it is commonly used in wastewater treatment. Practice has proved that in the operation need to pay attention to the following points: (1) neutralization and precipitation, the wastewater if the pH value is high, need to be neutralized before discharge; (2) wastewater often have a variety of heavy metals coexist, When the wastewater contains Zn, Pb, Sn, Al and other amphoteric metals, the pH value is high and there may be a tendency of redissolution. Therefore, the pH value should be controlled strictly and segmented precipitation should be carried out. (3) Some anions such as halogen, Cyanide, humus, etc. may form complexes with heavy metals, so to be pretreated before neutralization; (4) Some small particles, difficult to precipitate, you need to join the flocculant to aid precipitation. Sulfide precipitation method By adding sulfide precipitation agent so that heavy metal ions in the wastewater generated sulfide precipitation removed. Compared with the neutralization precipitation method, the advantages of the sulfide precipitation method are: the solubility of heavy metal sulfide is lower than the solubility of its hydroxide, and the pH value of the reaction is between 7-9, the treated wastewater is generally not neutralized. Sulfide precipitation method is the disadvantage of [2]: Sulfide precipitate small particles, easy to form colloidal; Sulfide precipitant itself in the water residue, acid generated hydrogen sulfide gas, resulting in secondary pollution. In order to prevent secondary pollution problems, British scholars have developed an improved sulfide precipitation method, which is selectively added to the waste water to be treated with sulfide ions and another heavy metal ions (the heavy metal sulfide ion balance than the concentration required The heavy metal contaminants removed have high equilibrium concentrations of sulfides). Since the added heavy metal sulfide is more soluble than the heavy metal sulfide in the waste water, the original heavy metal ions in the waste water are separated from the heavy metal ions added in the waste water at the same time, preventing the generation of hydrogen sulfide and the residual sulfide ions . Redox treatment Chemical reduction method Cr in electroplating wastewater mainly exists in the form of Cr6 + ions. Therefore, reducing agent Cr6 + is reduced to Cr3 + of micro-poison after adding reducing agent to waste water, and then lime or NaOH is added to produce Cr (OH) 3 precipitate to be separated and removed. Electroplating wastewater treatment by chemical reduction is one of the earliest applied treatment technologies. It has a wide range of applications in our country. The treatment principle is simple, the operation is easy to master, and can withstand the impact of large amount of water and high concentration of wastewater. According to the different reductant, it can be divided into FeSO4 method, NaHSO3 method, iron filings method, SO2 method and other chemical reduction method for the treatment of Cr-containing wastewater, alkalization generally use lime, but more waste; with NaOH, the sludge Less, but the high cost of drugs, processing costs, which is the shortcomings of chemical reduction. Ferrite method Ferrite technology is based on the principle of ferrite production developed. Excessive FeSO4 is added into the Cr-containing waste water to reduce Cr6 + to Cr3 + and Fe2 + to Fe3 +, and the pH value is adjusted to about 8 so that the Fe ions and the Cr ions produce the hydroxide precipitate. Into the air stirring and adding hydroxide continue to react, forming chromium ferrite. The typical process of intermittent and continuous process. The sludge formed by the ferrite method has high chemical stability and is easy to be separated by solid-liquid and dehydrated. In addition to ferrite ferrite treatment of waste water containing Cr, especially for heavy metal ions in the plating mixed wastewater. Ferrite method has been used for several decades in China. The treated wastewater can meet the emission standards and is widely used in the electroplating industry in China. Ferrite method has the advantages of simple equipment, less investment, easy operation, no secondary pollution and so on. However, it requires heating (about 70 degrees Celsius) during ferrite formation, high energy consumption, high salinity after treatment, and the inability to treat wastewater containing Hg and complex. Electrolysis Electrolytic treatment of Cr-containing wastewater in our country has more than 20 years of history, with high removal efficiency, no secondary pollution, the precipitation of heavy metals can be recycled and so on. About 30 kinds of metal ions in wastewater solution can be electrodeposited. Electrolysis is a relatively mature treatment technology, can reduce the sludge generation, and can recover Cu, Ag, Cd and other metals, has been used in wastewater treatment. However, the cost of electrolysis is relatively high, generally after electrolysis electrolysis better economic benefits. Solvent extraction and separation Solvent extraction [4] is a common method for separating and purifying substances. Due to liquid-liquid contact, continuous operation, the separation effect is better. When using this method, to choose a higher selectivity of the extractant, the heavy metals in wastewater generally exist in the form of cations or anions, for example under acidic conditions, complexing with the extractant, extraction from the aqueous phase to the organic phase , Then stripped back to the aqueous phase under alkaline conditions, regenerating the solvent for recycling. This requires careful attention to the selection of aqueous phase acidity during extraction. Although the extraction method has greater superiority, however, the loss of solvent during the extraction process and the energy consumption during the regeneration process make the method have some limitations and the application is greatly restricted. Adsorption method Adsorption method is to use the unique structure of adsorbent to remove heavy metals is an effective method. Adsorption of heavy metals used in the treatment of heavy metal wastewater adsorbent activated carbon, humic acid, sepiolite, polysaccharide resin. Activated carbon equipment is simple, widely used in wastewater treatment, but the regeneration efficiency of activated carbon is low, the treatment of water quality is difficult to achieve the reuse requirements, generally used for pretreatment of electroplating wastewater. Humic acid is a relatively cheap adsorbent, the humic acid made of humic acid resin used to deal with Cr, Ni-containing wastewater has a successful experience. Related research shows that chitosan and its derivatives are good adsorbents for heavy metal ions. After cross-linking, the chitosan resin can be reused for 10 times with no obvious decrease of adsorption capacity [5]. The use of modified sepiolite to treat heavy metal wastewater has good adsorption capacity for Pb2 ​​+, Hg2 + and Cd2 +, and the content of heavy metals in wastewater after treatment is significantly lower than the comprehensive discharge standard of sewage. Another literature reports that montmorillonite is also a good performance clay mineral adsorbent, aluminum zirconium pillared montmorillonite in acidic conditions of Cr6 + removal rate of 99%, the effluent Cr6 + content lower than the national emission standards, with the actual Apply the last heat Membrane separation technology Membrane separation is the use of polymers have the selectivity of the material separation techniques, including electrodialysis, reverse osmosis, membrane extraction, ultrafiltration and so on. Treatment of electroplating industrial electrodialysis wastewater treatment, wastewater composition unchanged, is conducive to back to the tank. Containing Cu2 +, Ni2 +, Zn2 +, Cr6 + and other metal ion wastewater treatment are suitable for electrodialysis, already complete sets of equipment. Reverse osmosis has been used extensively for Zn, Ni, Cr rinse water and mixed heavy metal wastewater treatment. Reverse osmosis treatment of electroplating wastewater, treated water can be reused, to achieve closed-loop. Liquid membrane treatment of electroplating wastewater research reports many, some areas of liquid membrane method has been from the basic theoretical research into the initial stage of industrial applications, such as China and Austria are using emulsion liquid membrane technology containing Zn wastewater, also used in Au-coated waste Liquid treatment [7]. Membrane extraction is an efficient, secondary-free separation technique that has made great strides in metal extraction. Ion exchange treatment method Ion exchange treatment method is the use of ion exchangers separation of harmful substances in waste water, the application of ion exchangers are ion exchange resins, zeolites, etc., ion exchange resins are gel type and macroporous type. The former is selective, the latter is complicated to manufacture, high in cost and large in consumption of regenerant, and thus is greatly restricted in application. Ion exchange is carried out by the exchangeable agent with its own free-moving ions and ions in the solution to be processed by ion exchange. The driving force for promoting ion exchange is the difference in concentration between ions and the affinity of the functional groups on the ion exchangers. In most cases, the ions are adsorbed and exchanged first, and the ion exchangers have both adsorption and exchange roles. The application of this material is more and more, such as bentonite [11]. It is a clay with montmorillonite as the main component. It has the advantages of good water absorption and swelling, large specific surface area, strong adsorption capacity and ion exchange capacity. Improved adsorption and ion exchange ability. However, natural zeolite has more advantages than bentonite in the treatment of heavy metal wastewater: zeolite [9] is an aluminosilicate mineral with grid structure, its internal porous, large specific surface area, unique Adsorption and ion exchange capacity. Studies have shown that the mechanism by which zeolites remove heavy metal ions from wastewater is, in most cases, a dual action of adsorption and ion exchange. With the increase of flow rate, ion exchange will take the place of adsorption. Pretreatment of native zeolite with NaCl increases adsorption and ion exchange capacity. By adsorption and ion exchange regeneration process, the concentration of heavy metal ions in wastewater can be concentrated by 30 times. Removal of copper zeolite, NaCl regeneration process, the removal rate of 97% or more, can be multiple adsorption exchange, regeneration cycle, and the copper removal rate does not decrease. 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October 15, 2021