As explained in the text Iron Corrosion Protection, some of the most used methods to protect iron and steel, and thus reduce the enormous damage caused by rusting, is electroplating and galvanizing.
Electroplating is a process in which the metal part you want to protect is coated with a more noble metal, which works as a a sacrificial metal, that is, this metal will have a higher oxidation potential than iron and, therefore, will oxidize in its place.
The sacrifice metals used can be gold, silver, nickel, copper, among others. If the metal used is zinc, the process is called galvanizing.
These processes can be quite harmful to the environment, because in addition to using a very large amount of water, they also generate toxic waste.
For example, in the electrodeposition of zinc, gold and silver, cyanide is used, which is extremely toxic.
The effluents from this process also generate toxic metal ions such as nickel cations (Ni2+) and copper (Cu2+).
A highly toxic heavy metal, even in small amounts, that is found in electroplating waste is cadmium. It is bioaccumulative, that is, it accumulates progressively along the food chain and is not eliminated over time. By contaminating humans, cadmium can cause kidney dysfunction, lung problems, rheumatic and myalgic pain, disorders metabolics leading to osteoporosis, in addition to being a carcinogen, causing genetic mutations, such as changing the system functions genital.
To reduce the environmental impacts of electroplating effluents, cyanide is usually oxidized to cyanate, which is less toxic and hydrolyses, producing ammonium and bicarbonate ions, in addition to ion precipitation metallic.
This procedure produces a solid waste in a very high amount and disposal with high costs. Therefore, in practice, most companies store this waste, as there is a large deficit of class I landfills, which are for hazardous waste.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/consequencias-galvanoplastia-para-meio-ambiente.htm
