Parkes process
Encyclopedia
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 300 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 the liquid lead, it can also be removed and isolated by the same process. The process was patented by Alexander Parkes
in 1850.
Silver
Silver is a metallic 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 element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, 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 solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid...
.
The process takes advantage of two liquid-state properties of zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
. The first is that zinc is immiscible with lead, and the other is that silver is 300 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
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
is present in the 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.-Biography:...
in 1850.