Pollution analysis of galvanizing process

- Sep 03, 2018 -

Zinc plating is one of the earliest electroplating processes in production and is the most widely used plating in the electroplating industry in China, accounting for more than 50% of the total electroplating. Zinc plating refers to the surface treatment technology that coats the surface of metal, alloy or other materials with a layer of metallic zinc for aesthetics and rust prevention.

There are many types of galvanizing processes, which can be divided into cyanide galvanizing and cyanide-free galvanizing according to their properties. The cyanide galvanizing process has good dispersing ability and covering ability, and the plating layer is smooth and meticulous, simple in operation, wide in application range, and long-term use in production. However, the cyanide galvanizing solution contains highly toxic cyanide, which does not pollute the environment and poses a threat or hazard to workers' health. At present, cyanide galvanizing has been listed as a phase-out process, and only a few products with special requirements such as military and aerospace are still in use. The cyanide-free zinc plating process includes alkaline zincate galvanizing, sulphate galvanizing and potassium salt galvanizing.

The pollutants produced by the galvanizing process mainly include zinc wastewater, acid-base exhaust gas and electroplating waste liquid. The wastewater mainly comes from the process of plating, galvanizing, and plate cleaning after galvanizing; acid waste gas (acid mist) and alkaline waste gas (alkali mist) are from galvanizing tank;

The electroplating waste liquid mainly includes electroplating liquid which is aged and scrapped, residual liquid removed by plating tank, and waste residue generated by filtration of plating liquid. The electroplating waste liquid belongs to hazardous waste, and the waste type is HW17, which needs to be disposed according to the treatment method prescribed by the state.

               Main pollutants in galvanizing process


        Galvanized

           Major pollutant
Exhaust gasWaste waterSolid waste






Galvanized

Zinc galvanizingAlkali mistZinc oxide, sodium hydroxide and some additives, brighteners, etc.Zinc-containing waste liquid
Sulfate zinc platingAcid mistZinc sulfate, thiourea and some brighteners, etcZinc-containing waste liquid
Potassium salt galvanizingAcid mistZinc chloride, potassium chloride, boric acid and some brighteners, etc.Zinc-containing waste liquid

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