Parkes method

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The Parkes process is a metallurgical separation process .

According to the inventor Alexander Parkes (1842), the silver from lead containing silver can be extracted by zinc . If lead containing silver is melted together with zinc, the latter removes the silver from the lead. If the zinc is used several times for desilvering, the result is a very silver-rich zinc, from which the zinc is separated by distillation , while the remaining silver still contains lead and is driven off . This is done using the parking procedure. The process is based on the different solubility of silver and lead in zinc. At temperatures of up to 400 ° C, the liquid lead and solid zinc are practically immiscible.

In a first process, the silver must be separated from most of the lead. First, zinc is added to the molten lead at temperatures higher than 400 ° C. The mixture is then cooled. Since silver is easily soluble in molten zinc, it changes into the zinc phase. The zinc melt then solidifies as zinc foam (zinc-silver mixed crystals). This allows the silver to be separated from most of the lead. This zinc foam is also known as arm lead. It is then heated to the melting point of the lead (327 ° C) so that some of the lead melts and can be removed. The remaining zinc-lead-silver melt is then heated to the boiling point of zinc (908 ° C) and the zinc is distilled off. The product obtained in this way is called rich lead and contains approx. 8–12% silver.

literature

  • Percy John: The metallurgy of lead: Including desilverisartion and cupellation . 1870, p. 148 ( books.google.de ).
  • E. Henglein and H. Nowotny: On the basis of the Parkes process . In: Monthly magazine for chemistry . tape 79 , no. 6 , 1948, pp. 629-637 , doi : 10.1007 / BF00898700 .

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