Lead Background Data

Scientific Data

Notable Characteristics

Lead has a bright lustre and is a dense, ductile, very soft, highly malleable, bluish-white metal that has poor electrical conductivity. It is also highly resistant to corrosion and because of this property is used to contain corrosive liquids (e.g. sulphuric acid).

History

Humans have used lead for at least 7,000 years mainly because deposits containing lead are widespread and it is easy to extract and work with. Lead was mentioned in the book of Exodus. Alchemists thought that lead was the oldest metal and associated it with the planet Saturn. Lead pipes bearing the insignia of Roman emperors are symbol in service today in some countries. Lead’s symbol Pb is an abbreviation of its Latin name plumbum. The English word plumbing also derives from this Latin root.

Occurrence

Lead is usually found in ore with zinc, silver and copper and is extracted together with these metals. The main lead mineral is galena (PbS). Other common varieties include cerussite (PbCO3) and angelsite (PbSO4).

Zinc Background Data

Scientific Data

Notable Characteristics

Zinc is a moderately reactive metal that will combine with oxygen and other non-metals and will react with dilute acids to release hydrogen.

History

The earliest use of zinc was in brass where it is alloyed with copper. This use probably arose accidentally when zinc-containing raw materials were reduced with charcoal in a copper crucible. These developments cannot be precisely dated but were well developed by 20 BC when the Romans were using brass in coinage. Experimental observations in Greece and Babylon predate this widespread use by at least two centuries. It is likely that the bronzes that lent their name to the archaeological age of 3000 BC – 1000 BC contained some zinc by accident or design. Brass was also known in India and China early in their recorded histories.

Occurrence

The world is naturally abundant in zinc. It is estimated that the first mile of the earth’s crust under land contains 224,000,000 million tonnes of zinc. Such estimate, however, take no account of whether or not it is economic or environmentally acceptable to exploit these resources.

The most common zinc mineral is sphalerite also known as zinc blende. This mineral crystallises from the hydrothermal solution as pure zinc sulphide and is found in almost all currently mined zinc deposits. Zinc is often mined in association with lead, copper, silver and other metals.