Electrolysis. Electrolysis uses currents to give the energy needed to help a chemical reaction occur to break apart chemical bonds between metals and impurities. This method was first used in the late 18th century to separate tin and zinc from their salts. This method is also used for purifying aluminum.

Refining of silver by Cupellation:

Cupellation is a refining process in metallurgy, where ores or alloyed metals are treated under very high temperatures and controlled operations to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth, present in the ore or alloy.

The steps involved in the refining of silver by cupellation are:

1. Melting of the silver ore:

The first step involves melting the ore to remove impurities like lead, copper, zinc, arsenic, antimony or bismuth, present in it.

2. Addition of lead:

After melting, lead is added to the melted ore to form an alloy. Lead is added in excess so that all the silver present in the ore is converted into an alloy with lead.

3. Cupellation:

The alloy is then heated in a cupel, which is a small porous cup made of bone ash or magnesium oxide. The cupel absorbs the base metals, leaving behind only the noble metals, like gold and silver.

4. Oxidation:

The cupel is heated to a very high temperature of around 1000°C, in the presence of a strong draft of air or oxygen. The lead in the alloy gets oxidized to form lead oxide (PbO) and gets absorbed by the cupel.

5. Removal of lead:

The process of absorbing the lead oxide by the cupel is called cupellation. The cupel is then cooled, and the lead oxide is scraped off from its surface.

6. Collection of silver:

The remaining alloy in the cupel is then heated again, and the silver present in it melts and is collected in a separate container.

7. Purification of silver:

The collected silver is further purified by electrolysis or by boiling it with nitric acid to remove any remaining impurities.

Thus, cupellation is an important process for refining silver and other noble metals, and it is widely used in the metallurgical industry.