Talking about the treatment of electroplating waste gas

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This paper analyzes the types and hazards of electroplating waste gas, and proposes some specific measures to reduce, control and purify electroplating waste gas. The clean electroplating production process should be actively adopted to reduce the generation of electroplating waste gas from the source.

This paper analyzes the types and hazards of electroplating waste gas, and proposes some specific measures to reduce, control and purify electroplating waste gas. The clean electroplating production process should be actively adopted to reduce the generation of electroplating waste gas from the source.

Electroplating is a small but essential basic technological industry in the national economy, and it is also a heavy polluting industry. The exhaust gas, waste water and waste residue produced by electroplating seriously affect people's life and health. In recent years, the number of electroplating factories and points in the southeast coast and the more economically developed inland areas has been increasing, and the scope of electroplating processing has continued to expand. There is no doubt that the amount of electroplating "three wastes" is also increasing, and the environmental pollution in the location of electroplating is also increasing. If no measures are taken to control these waste gases, they will cause pollution to human beings and the environment. Based on years of experience in electroplating process design, I put forward some relevant suggestions and measures for electroplating waste gas treatment, which provide technical reference for electroplating industry waste gas control, and are of great significance to protect the ecological environment and control air pollution.

1. Types and hazards of electroplating waste gas

1.1 Types of electroplating waste gas

There are many types of electroplating. In addition to the four conventional types of zinc plating, copper plating, nickel plating and chrome plating, there are also widely used zinc-nickel, zinc-cobalt, zinc-iron alloy electroplating, copper-zinc, copper-tin, Copper-zinc-tin imitation gold plating, nickel-zinc, nickel-tin black plating, as well as gold, silver, tin and even a small amount of rare metals to meet the special needs of some IT industries and certain products in the electronics industry Ruthenium, rhodium, palladium, indium plating, etc. At the same time, there will be metal oxidation, phosphating, passivation and other surface treatments. The various additives and complexes in the formulation of these process solutions are dazzling. In addition, there are still a few types of plating that cannot eliminate cyanide in the short term, so cyanide-containing electroplating still exists in the electroplating of some special products. In particular, the increase in the amount of acid and alkali during surface treatment such as pre-plating and stripping will inevitably generate a large amount of waste gas in the electroplating production process. Among them are some metal dust, acid-base waste gas, organic waste gas, chromic acid mist and various waste gases emitted from heating of various electroplating baths, including ammonia-containing waste gas and cyanide-containing waste gas.

1.2 Hazards of electroplating exhaust gas

The harm of electroplating waste gas to the human body is mainly manifested in the harm to the human respiratory tract, eyes, and skin. Some electroplating waste gas is colorless and odorless, causing long-term and chronic damage to the respiratory tract. After gradual accumulation, the content exceeds the limit, which will lead to bronchitis and bronchial asthma. , lung cancer, liver cancer and other diseases. The hydrogen chloride and acid-base mist discharged from the electroplating process will irritate the eyes and skin of the human body, causing symptoms such as pink eye and dermatitis. The harm to plants and buildings in the township, the sulfur oxides and nitrogen oxides emitted by the electroplating process, have a harmful effect on the growth of plants in the air, and even kill plants. If acid rain is formed, it will also cause corrosion and rust to buildings.

In addition to the above hazards, during the electroplating process, the generated electroplating exhaust gas will also harm the electroplated products. The main reason is that in the electroplating workshop, too much acid-base mist, dust, etc., will affect the performance of electroplating equipment and the purity of electroplating materials in the workshop to varying degrees.

2. Treatment method of electroplating waste gas

According to the "Emission Standard of Electroplating Pollutants" (GB21900-2008), the electroplating process and facilities must install a local gas collection system and carry out centralized purification treatment before they can be uniformly discharged into the atmosphere from the exhaust pipe (thus, the electroplating waste gas can be passed through There are three ways to deal with it, namely reducing electroplating exhaust gas at the source, installing an exhaust system, and installing electroplating exhaust gas purification equipment.

2.1 Reduce the generation of exhaust gas from the source

(1) In the process of alkali washing and degreasing, acid washing and descaling or descaling before electroplating, alkali mist inhibitor and acid mist inhibitor can be added to the solution respectively, so as to greatly reduce the escape of alkali mist and acid mist. . At the same time, a narrow and movable windshield can be added on both sides of the notch of each electroplating tank, in addition to covering the anode hook, anode plate and heater, the tank surface looks neat and tidy, and it is more suitable for The exhaust effect of the tank side can be enhanced due to the reduction of the tank liquid area, thereby reducing the pollution of the exhaust gas to the workshop environment.

(2) When removing the oxide scale on the steel parts, 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 cleaning with mixed acid (sulfuric acid plus nitric acid) or stripping with nitric acid, the generation of nitrogen oxides can be suppressed and reduced by adding a small amount of urea. Simply using nitric acid for pickling and stripping is not recommended.

(4) Adding a small amount of F-53 (perfluoroalkyl ether sulfonate) to the chrome plating tank can inhibit the generation of chromic acid mist. If there are polyethylene or polyvinyl chloride hollow plastic balls floating on 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 waste gas, the polluted waste gas can be transported to the gas purification system by installing an exhaust 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 ​​electroplating plants is generally large and belongs to the same production process. The staff are distributed in the whole room. In order to maintain a certain negative pressure in the room, mechanical air supply with comprehensive ventilation should be used. The sources of pollutants are some electroplating tanks. During the working process, the pollutants will be directly released from the electroplating tanks. Therefore, it is only necessary to perform local exhaust air for each electroplating tank, and then process the quality according to the regulations. After reaching the standard, it is discharged to the outside. In order to exhaust the air evenly and reduce the resistance of the ventilation and exhaust system, the turns and three-way connections of the air duct should be designed along the airflow direction. 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 of acid waste gas purification is to spray the acid waste gas with three-stage lye, and then discharge it from the chimney. The gas is discharged and enters the spray tower with packing. The efficiency of the process for removing acid waste gas can reach more than 90%.

3. Conclusion

In the electroplating industry, the discharge of "three wastes" is very serious. To reduce the discharge of "three wastes", on the one hand, it is necessary to improve the process flow, improve the electroplating production technology from the source, and reduce the discharge of pollutants from the first step of industrial production; at the same time, also To purify the discharged pollutants, through research and analysis of the nature of the pollutants, use chemical, physical, biological and other methods to remove the pollutants, and finally meet the pollutant discharge standards to ensure that the environment is not polluted.