Question

Write short notes on cupellation.

Answer 1

1. Cupellation is a refining process used primarily for purifying silver from its alloys, especially from lead-silver alloys.
2. The impure silver is heated in a special porous crucible called a cupel, made of bone ash.
3. The process takes place in a reverberatory furnace where a blast of air is passed over the molten metal.
4. Lead, which is an impurity, gets oxidized to lead oxide (PbO) due to the air blast.
5. The lead oxide is absorbed by the cupel or blown away, leaving behind pure, shining silver.
6. This method is effective because the oxidation of lead is easier than that of silver, allowing selective removal of impurities.
7. Cupellation is a key step after the Parkes process for silver extraction from argentiferous (silver-containing) lead.
8. This process ensures the removal of lead impurity and recovery of pure silver.