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Electroplating is a small but essential basic technological industry in the national economy. At the same time, it is a heavily polluting industry. The waste gas, waste water and waste generated by electroplating seriously affect people's lives and health. In recent years, in the southeastern coastal areas and the more developed economies, the number of electroplating plants and points has been increasing, and the scope of electroplating processing is expanding. There is no doubt that the amount of “three wastes†generated by electroplating is also increasing, and the environmental pollution at the place where plating is applied is intensifying. If these waste gases are not treated, they will cause pollution to humans and the environment. Based on years of experience in electroplating process design, I have put forward some suggestions and measures for electroplating waste gas treatment, which provide technical reference for waste gas control in electroplating industry, and have important significance for protecting ecological environment and controlling air pollution.
1 Types and hazards of electroplating exhaust gas
1.1 Types of electroplating exhaust gas
There are many types of electroplating, in addition to galvanizing, copper plating, nickel plating, and chrome plating, there are also widely used zinc-nickel, zinc-cobalt, zinc-iron alloy plating, copper-zinc, copper-tin, Copper-zinc-tin-gold plating, nickel-zinc, nickel-tin black plating, and gold plating, silver plating, tin plating, and at least precious metals for the special needs of some IT industries and certain products in the electronics industry.钌, 铑, palladium, indium plating, etc. At the same time, there are surface treatments such as oxidation, phosphating, and passivation of metals. The various additives and complexes in the formulation of these process solutions are dazzling. In addition, there are still a few platings that can't eliminate cyanide in the short term, so cyanide-containing plating still exists in some special product plating. Especially in the surface treatment before plating and the increase in the amount of acid and alkali during deplating, these eventually inevitably generate a large amount of exhaust gas in the electroplating production process. Among them, there are a variety of exhaust gases, including ammonia-containing waste gas and cyanide-containing waste gas, which are emitted from metal dust, acid-base exhaust gas, organic waste gas, chromic acid mist and various plating baths.
1.2 The harm of electroplating waste gas
The harm of electroplating exhaust gas to the human body is mainly manifested in the harm to the human respiratory tract, eyes and skin. Some electroplating exhaust gases are colorless and odorless, causing long-term chronic damage to the respiratory tract. After gradually accumulating, the content exceeds the limit, which may lead to bronchitis and bronchial asthma. , lung cancer, liver cancer and other diseases. The hydrogen chloride, acid-base mist, etc. emitted by the electroplating process may cause irritation to human eyes and skin, and may cause symptoms such as pink eye and dermatitis. The danger to plants and buildings in the township, the sulphur oxides and nitrogen oxides emitted by the electroplating process are harmful to the growth of plants in the air, and even kill plants. If acid rain is formed, it will cause corrosion, rust, etc. to the building.
In addition to the above hazards, the electroplating exhaust gases produced during the electroplating process can also cause damage to the electroplated products. Mainly because in the electroplating workshop, too much acid-base fog, dust, etc., will have different effects on the performance of electroplating equipment and the purity of electroplating materials in the workshop.
2 treatment method of electroplating waste gas
According to the "Electroplating Pollutant Emission Standards" (GB21900-2008), the electroplating process and facilities must be installed with a local gas collection system and centralized purification treatment in order to uniformly discharge the exhaust gas into the atmosphere (thereby passing the electroplating exhaust gas) Three ways to control, respectively, reduce the plating exhaust gas, install the exhaust system, and install the electroplating exhaust gas purification equipment.
2.1 Reduce the generation of exhaust gas from the source
(1) In the process of alkali washing, pickling, descaling or descaling before electroplating, an alkali mist inhibitor and an acid mist inhibitor may be separately added in the solution, thereby greatly reducing the escape of alkali mist and acid mist. . At the same time, a narrow, movable windshield can be added on both sides of the notch of each plating tank. In addition to covering the anode hook, the anode plate and the heater, the groove surface is neat and tidy. The reduction of the visible bath area enhances the exhaust effect of the groove side, thereby reducing the pollution of the exhaust gas to the workshop environment.
(2) When the scale on the steel parts is removed, the shot peening process can be used to replace part of the chemical pickling or the acid-free pickling process, so that the generation of acid waste gas can be greatly reduced at the source.
(3) For copper parts, when washing with mixed acid (sulfuric acid plus nitric acid) or deplating with nitric acid, the generation of nitrogen oxides can be suppressed and reduced by adding a small amount of urea. It is not recommended to use pure nitric acid pickling and deplating.
(4) The addition of a small amount of F-53 (perfluoroalkyl ether sulfonate) to the chrome plating tank suppresses the generation of chromic acid mist. If there is a polyethylene or polyvinyl chloride hollow plastic ball floating in the liquid surface in the chrome plating tank, the fog suppression effect will be better.
2.2 Installation of exhaust system and purification system
Considering the treatment of electroplating exhaust gas, the exhaust gas system can be installed to transport the polluted exhaust gas to the gas purification system to achieve the purpose of removing toxic and harmful gases. It can be seen that the installation of the exhaust system and the purification system is a unified whole.
The area of ​​the electroplating plant is generally large and belongs to the same production process. The staff is distributed throughout the room. In order to maintain a certain negative pressure inside the room, a fully ventilated mechanical air supply should be used. The source of the pollutants are some electroplating tanks. During the working process, the pollutants will be directly released from the plating tank. Therefore, it is only necessary to partially exhaust the respective electroplating tanks, and then process them according to the regulations, and then discharge them to the outside after reaching the standard. In order to evenly exhaust the air and reduce the resistance of the air exhaust system, the turning of the air duct and the three-way connection should be designed along the airflow. In order to adjust the reasonable air volume, the damper can also be adjusted in the air duct.
In the treatment of acid waste gas, the main method for purifying the acid waste gas is to spray the acid waste gas with the third-grade alkali liquid, and then the chimney is discharged. When the acid waste gas is absorbed by the method, the closed cover is installed on the vacuum air pump, and the inside of the workshop is installed. The gas is discharged into the spray tower with the packing. The efficiency of the process for removing acid waste gas can reach more than 90%.
3 Conclusion
In the electroplating industry, the “three wastes†emissions are very serious. To reduce the emissions of “three wastesâ€, on the one hand, we must improve the process from the source, improve the electroplating production technology, and reduce the pollutant emissions from the first step of industrial production; To purify the pollutants discharged, through research and analysis of the nature of the pollutants, chemical, physical, biological and other methods to remove pollutants, and finally meet the pollutant discharge standards to ensure that the environment is not polluted.
Talking about the treatment of electroplating exhaust gas
This paper analyzes the types and hazards of electroplating exhaust gas, and proposes some specific measures to reduce, treat and purify electroplating exhaust gas. The clean plating production process should be actively adopted to reduce the generation of electroplating exhaust gas from the source.