Parkes process

The Parkes process is a pyrometallurgical industrial process for removing silver from lead during the production of bullion. It is an example of liquid–liquid extraction.

The process takes advantage of two liquid-state properties of zinc. The first is that zinc is immiscible with lead, and the other is that silver is 3000 times more soluble in zinc than it is in lead. When zinc is added to liquid lead that contains silver as a contaminant, the silver preferentially migrates into the zinc. Because the zinc is immiscible in the lead it remains in a separate layer and is easily removed. The zinc-silver solution is then heated until the zinc vaporizes, leaving nearly pure silver. If gold is present in the liquid lead, it can also be removed and isolated by the same process.[1]

The process[2] was patented by Alexander Parkes in 1850.[3][4][5][6] Parkes received two additional patents in 1852.[7]

The Parkes process was not adopted in the United States, due to the low native production of lead.[8] The problems were overcome during the 1880s and by 1923 only the Parkes process was used.[9]

See also


  1. Pauling, Linus General Chemistry W.H.Freeman 1947 ed.
  2. "Parkes process (chemistry)". Britannica Online Encyclopedia. Britannica Online Encyclopedia. Retrieved 2009-08-20.
  3. Tylecote, R. F (1992). "A history of metallurgy": 158. ISBN 978-0-901462-88-6.
  4. Percy, John (1870). The metallurgy of lead: Including desilverisartion and cupellation. p. 148.
  5. Office, Patent (1861). Patents for inventions. Abridgments of specifications.
  6. Patent Office, Great Britain (1867). Patents for inventions: Abridgments of specifications : Class.
  7. Patent Office, Great Britain (1861). Patents for inventions: Abridgments of specifications : Class.
  8. Eurich, Ernst (December 1912). Joseph Struthers, ed. "The Development of the Parkes Process in the United States". Bulletin of the American Institute of Mining Engineers. The American Institute of Mining Engineers (72): 1531–1540.
  9. Rowe, David John (1983-07-01). Lead Manufacturing in Britain: A History. pp. 189–190. ISBN 978-0-7099-2250-6.
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