U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
  
Reaction of Arsenic Minerals and Gold Ores with Alkaline Cyanide
Solutions
by
Walter H. Ficklin (U.S. Geological Survey, Denver, Colo.), Geoffrey
S. Plumlee (U.S. Geological Survey, Denver, Colo.), and John B. McHugh (U.S.
Geological Survey, Denver, Colo.)
Abstract
Gold ores often contain significant quantities of arsenic
(As). The As may occur in several different mineral
forms and/or oxidation states. The most common As minerals are
arsenopyrite (FeAsS), orpiment (As2S3), and
realgar (AsS) but some deposits may contain oxidized forms
of arsenic (arsenates) and more exotic minerals, such as enargite
(Cu3AsS4). During heap leaching with alkaline
cyanide solutions, some As is dissolved from these minerals.
At pH values equivalent to those found in heap-leach solutions,
the presence of cyanide increases the concentration of
arsenic that dissolves by a factor of 4 to 100 for various forms
of As. Formation of thiocyanate is one factor that enhances
the dissolution of arsenic from sulfide minerals. Orpiment reacts
more strongly with cyanide solutions than realgar and
much more strongly than arsenopyrite.
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