Gold Recovery by Heap Leaching
Gold Recovery by Heap Leaching
That presumes that the only elements are the gold, Sodium
Cyanide and water
Catalyst to Gold Dissolution
Once the gold has been dissolved in the cyanide, and the ore
body has been reasonably depleted of its gold, there are two main
processes for recovering the gold from the pregnant cyanide
solution. One is the Merrill-Crowe zinc precipitation process and
the other is the adsorption of the gold onto activated carbon. The
oldest method, Merrill Crowe, involves first removing the
oxygen from the solution, then mixing a fine zinc powder with it
(-200 mesh), and recovering the very fine gold precipitate on a
precoat filter, since the gold precipitate is very fine, ranging from
a few microns to 50 or so microns.
1. Merrill-Crowe Recovery
Zinc powder is then added to the solution with a dry chemical feeder
and a zinc emulsification cone. The reaction of the special fine
powder zinc with the solution is almost instantaneous.
Other chemicals have been used to leach gold, and they include
bromine, chlorine, and thiourea. There has also been a lot of
experimentation with various biological media for recovering
gold from ores, but no one has come up with a more cost
effective and productive method than leaching with cyanide. In
some special circumstances, some of the other methods may
show promise, but for a good oxide gold ore, CN leaching is
usually the best of the leach methods for the yellow precious
metal.
The Advantages in Heap Leaching: