Zinc refining is the process of purifying
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
to ''special high grade'' (SHG) zinc, which is at least 99.995% pure.
This process is not usually required when smelting of zinc is done through
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
processes, but is needed when zinc is produced by
pyrometallurgical processes, because it is only 98.5% pure.
There are various refining methods, but the refluxing process is the most commonly used.
High purity zinc is required industrially to avoid
zinc pest, a slow distortion and cracking of zinc die castings caused by impurities precipitating out.
Refluxing process
The
New Jersey Zinc Company
New is an adjective referring to something recently made, discovered, or created.
New or NEW may refer to:
Music
* New, singer of K-pop group The Boyz
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* ''New'' (album), by Paul McCartney, 2013
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invented this process in 1930.
The process take advantage of the relatively low boiling point of zinc () as compared to the impurities being removed in the first "column":
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
and
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
. Therefore, in the first column the zinc is heated above its boiling point and allowed to rise to a condenser. The iron and aluminium impurities sink to the bottom in the form of a solid or liquid. There are still
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
and
cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
vapor impurities. In order to remove the lead 2-3% of the vapor is condensed, which draws the majority of the lead out of the vapor; down to the point where it is only 0.003% of the total contents. Finally the vapor is pumped into the cadmium column where it is cooled to an intermediate temperature below the boiling point zinc, but still above the boiling point of cadmium (). The zinc leaves out the bottom as a refined liquid, while the cadmium leaves out the top as vapor.
See also
*
Zinc smelting
*
ZAMAK
ZAMAK (or Zamac, formerly trademarked as MAZAK) is a family of alloys with a base metal of zinc and alloying elements of aluminium, magnesium, and copper.
Zamak alloys are part of the zinc aluminium alloy family; they are distinguished from the ...
References
Sources
*{{Citation , last = Porter , first = Frank , title = Zinc Handbook: Properties, Processing, and Use in Design , publisher = CRC Press , pages = 21–22 , year = 1991 , url = https://books.google.com/books?id=laACw9i0D_wC , isbn = 0-8247-8340-9.
Metallurgical processes
Zinc