Mercury removal in the gold-cyanide process

In the gold-cyanide process (GCP), the cyanide anions act to solubilize the gold and silver present in the ore. However, mercury is also solubilized in the process. The resulting mercury and cyanide-rich effluent is a serious health and environmental problem. Until now, there has been no known mercury treatment available that could be used effectively in the pH ∼10 solutions. Recently, however, the author developed a new chelate ligand that can be used to precipitate Hg from NaCN solutions at this pH level. On an actual sample taken from an active gold mine, the chelate selectively reduced the mercury level from 34.5 to 0.008 ppm within 15 minutes. Importantly, the gold and silver levels remained unchanged throughout this process. Thus, the environmental impact of Hg released by the GCP can be drastically reduced. Moreover, with a mercury treatment technology now available, it may be possible to change, or reinvent, the entire GCP process.