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The Parkes process is a pyrometallurgical industrial process for removing silver
Silver

Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....
 from lead
Lead

Lead is a main-group Chemical element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metal ....
, during the production of bullion. It is an example of liquid-liquid extraction
Liquid-liquid extraction

Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubility in two different miscible liquids, usually Water and an solvent....
.

The process takes advantage of two liquid-state properties of zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
. 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. Hence when zinc is added to liquid lead that contains silver as a contaminant, the silver preferentially migrates into the zinc.






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The Parkes process is a pyrometallurgical industrial process for removing silver
Silver

Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....
 from lead
Lead

Lead is a main-group Chemical element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metal ....
, during the production of bullion. It is an example of liquid-liquid extraction
Liquid-liquid extraction

Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubility in two different miscible liquids, usually Water and an solvent....
.

The process takes advantage of two liquid-state properties of zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
. 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. Hence when zinc is added to liquid lead that contains silver as a contaminant, the silver preferentially migrates into the zinc. Because the zinc remains in a separate layer, it is easily removed. The zinc-silver solution is then heated until the zinc volatilizes, leaving nearly pure silver. If gold is present in liquid lead, it can also be removed and isolated by the same process. The process was patented by Alexander Parkes
Alexander Parkes

Alexander Parkes was a metallurgist and inventor from Birmingham, England. He created Parkesine, the first man-made plastic.The son of a brass lock manufacturer, Parkes was apprenticed to a brass foundry at Messenger and Sons before going to work for George Elkington, who patented the electroplating process....
 in 1850.

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