Question

Describe the principle involved in the Parke’s process used for the extraction of silver.

Answer 1

1. Parke’s process is used to extract silver from argentiferrous lead (lead containing silver, about 1%).
2. It is based on the following principles:
   1. Molten lead and molten zinc are nearly immiscible (do not mix).
   2. Molten zinc is lighter and forms the upper layer; lead is heavier and forms the lower layer.
   3. Silver is more soluble in molten zinc than in molten lead.
   4. Zinc-silver alloy solidifies earlier than molten lead.
   5. Zinc is volatile and can be separated by distillation.
3. The argentiferrous lead is melted and mixed with molten zinc. Silver dissolves in zinc and rises to the top as an alloy.
4. On cooling, the silver-zinc alloy solidifies on top, while lead remains molten below.
5. The silver-zinc alloy is skimmed off and the process is repeated to recover more silver.
6. Zinc is separated from silver by distillation, leaving behind impure silver.
7. Further purification of silver is done by cupellation.