In his book "The Extractive Metallurgy of Gold", published 1991
by Van Nostrand Reinhold, ISBN 0 442 31797 2, the author J.C.
Yannopoulos writes :
"The solubility of gold in an aqueous solution of potassium
cyanide was known by alchemists of the 18th century. J.W. Mellor
(1923) specifically mentions that Scheele, in 1783, and Bagraton,
in 1843, noted that aqueous solutions of alkali cyanide could
dissolve gold. Potassium cyanide was mainly used to prepare
the electrolyte necessary for electroplating gold and silver by
the Elkington process, patented in 1843.
"However, L. Elsner was the first to realise the importance
of oxygen in the dissolution of gold and silver by aqueous
solution of potassium cyanide in 1846......
"Metallurgists....experimented with alkali cyanides as gold
solvents for the next 40 years, obtaining results of little or no
practical importance. It was J.S. MacArthur and his coworkers
R.W. Forrest and W. Forrest who first grasped the practical
importance of cyanide leaching of auriferous ores...in 1887.
MacArthur and the Forrest brothers patented the dissolution of
gold from ground ores by a weak cyanide solution. They also
patented its subsequent precipitation from the pregnant
solution by zinc shavings, and thus radically changed the
gold extraction process."
I believe it is true to say that, had the MacArthur/Forrest
process not been introduced when it was, the South African
gold mining industry would have collapsed in the 1890s.
Tony Brewis
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