Zinc (Zn) is a chemical element with atomic number 30 and located in group 12 of the periodic table of the elements. It is one of the least common metals and accounts for about 0.0075% of the earth's crust. It is found in the form of minerals, e.g. blende (zinc sulphides), calamine (silicates) and smithsonite (carbonate).
Zinc is obtained through mining activities in underground deposits or open fields. Once the rock is obtained, it is crushed. Then, the flotation process begins to obtain the zinc concentrate. Iron-rich ores are treated in a dry process. They are first roasted to transform them into oxide sulphide and then the content is reduced to carbon like coal, obtaining the metal. Another way of doing this, which would be cheaper and easier, would be to reduce the zinc oxide with charcoal. In a wet process, the oxide is roasted and then leached with dilute sulphuric acid. The lyes obtained have to be purified by separating the different phases present. It is then subjected to electrolysis, creating plates a few millimetres thick, which are removed from time to time. The cathodes obtained are melted and the metal is strained in order to be marketed.
Characteristics of zinc
Zinc is sometimes classified as a transition metal, although it is not. These are some of its characteristics and properties:
- It is bluish-white in colour.
- When there is humidity, a superficial layer of oxide or basic carbonate is formed, which insulates the metal and protects it from corrosion.
- It melts at 420ºC and has a density of 7140 kg/m3.
- It has a high resistance to cold plastic deformation, in fact, rolling has to be done above 100 °C.
- Pure zinc is malleable and ductile and can be rolled and tensioned. However, it can break if small amounts of other contaminating metals are present.
- It is a good conductor of electricity and heat, although pure zinc is not ferromagnetic.
Types of alloys
The most common alloys are as follows:
- Brass: this is the best known alloy of zinc (copper + zinc).
- Nickel silver: it is also known as maillechort or argentan, and is an unalterable alloy (copper + zinc + nickel).
- English metal: zinc + antimony base, it is a mixture that also contains tin, antimony, copper and sometimes lead.
- Tombac: copper and zinc base, i.e. brass + tin.
- Zamak: is the trade name for the alloy based on zinc, aluminium, magnesium and occasionally copper.
Zinc can be recycled without losing its physical and chemical properties. Zinc can be recycled from scrap brass products, scrap from galvanising and scrap zinc parts. Zinc coated steel scrap is generally produced from scrap from manufacturing processes and scrap from obsolete products. Almost 30% of the zinc consumed is obtained from recycling and currently 90% of the metal that can be recycled is recycled.
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