One primary method for extracting silver, particularly from lead ores, is a high-temperature process known as cupellation.
Understanding Cupellation
Cupellation is an ancient metallurgical process that is still utilized today to separate precious metals, like silver, from base metals, such as lead. It relies on the principle that under intense heat and controlled conditions, lead oxidizes and is absorbed by a porous material, leaving the non-oxidizing precious metal behind.
The Cupellation Process Steps
When extracting silver from lead ores in large furnaces, the cupellation process involves several key stages:
- Heating the Crushed Ore: The process begins by heating crushed ore containing silver until it melts. This heating is performed on a porous bed, which is traditionally made of bone ash.
- Absorption of Impurities: As the ore melts, the base metals, primarily lead and other impurities, are oxidized. The porous bed of bone ash then absorbs these oxidized impurities.
- Drawing Off Molten Silver: The molten silver, which does not oxidize and is not absorbed by the bone ash, remains on the surface of the porous bed. This purified molten silver is then carefully collected or drawn off.
This method effectively separates the valuable molten silver from the unwanted lead and other impurities, leaving a much purer form of silver.
