Abstract:
Under similar circumstances in a controlled but realistic setting, gold recovery with the mercury-free method was equal to or up to 40% higher than with the locally used amalgamation method but took 9 minutes longer.
Another possible factor that might have biased the results in favor of the amalgamation method is that the ore was dry milled. Dry milling is extremely dusty. Thus, ore dust containing gold is lost to the environment during milling and unloading of the mill.
Dry milling was used for both methods for a thorough comparison. Dry milling likely resulted in a loss of a small amount of gold and thus biased the results in favor of the amalgamation method.
The main downsides to dry milling are health-related complications, as inhaling the fine-grained dust may lead to silicosis. Furthermore, dry milling is much noisier than wet milling, which may cause reduced hearing among the miners and people living close to the processing stations.
There are several possible reasons why the gold yield was higher with direct smelting. One is that mercury does not catch all of the very fine-grained gold, which is then lost to the environment. Another reason is that concentrating gold in a washing tub is not as effective as in a gold pan, and small grains of gold might be lost to the tailings.
