A chemical element. Lead is a metal. It has the symbol Pb (from the Latin Plumbum) and atomic number 82 in the periodic table.
Lead has been used by humans for at least 7000 years, it was widespread and easy to extract, as well as easy to work with, being both highly malleable and ductile as well as easy to smelt. Currently lead is usually found in ore with zinc, silver and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is galena (PbS), which contains 86.6% lead. Other common varieties are cerussite (PbCO3) and anglesite (PbSO4). But more than half of the lead used currently comes from recycling.
Extraction
When it is mined the ore is extracted by drilling or blasting and then crushed and ground. The ore is then taken through a process developed in Australia in the 19th Century at Broken Hill. A flotation process separates the lead and other minerals from the waste rock (tailings) to form a concentrate by passing the ore, water and certain chemicals through a series of tanks in which the slurry is constantly mixed. Air is blown through the tanks and lead sulphides attatch to the bubbles and rise to form a foam which can be removed. The foam (which is around 50% lead) is dried and then sintered before being smelted to produce a 97% lead concentrate. The lead is then cooled in stages which causes the lighter impurites (dross) to rise to the surface where they can be removed. The molten lead bullion is then refined by additional smelting with air being passed over the lead to form a slag layer containing any remaining impurities and producing 99.9% pure lead.
Lead is the fourth most widely used metal after aluminium, copper and zinc. Common uses include: in lead-acid batteries, in electronic components, cable sheathing, ammunition, in the glass of CRTs, ceramics, leaded glass (see glass making), lead piping (not much lead piping these days, although leaded solder was legal for use on drinking water pipes into the 1980s (US)), in paint (banned since 1978 in the US, although older painted surfaces could be up to 50% lead by weight), casting alloys, pewter, solder, and dentistry filling. Also used as flashing on roofing to protect joins from rain. In petrol as tetra-ethyl lead and tetra-methyl lead to reduce knocking (also called pre-detonation, pre-ignition or pinking) from the 1920s, in 1999 leaded petrol was banned from sale in the EU.
Lead is a poisonous metal, it can damage nervous connections (especially in young children) and cause blood and brain disorders. The concern about lead's role in mental retardation in children has brought about widespread reduction in its use. Its historical use by the Roman Empire for piping is considered by some to be the cause for the dementia that affected many of the emperors.
The lead in pencils is actually carbon graphite
External Link:
Los Alamos National Laboratory's Chemistry Division: Periodic Table - Lead
See: Periodic Table