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Pb, A. Jonathan Buhalis
LEAD
by Jonathan Buhalis

History

Lead is one of the seven metals of antiquity (along with copper, gold, iron, mercury, silver, and tin). It rarely occurs naturally, but is easily extracted from its ore, galena (lead sulfide). Being soft, dense, and easily melted, lead has been used throughout history for weights and molds.

The Romans used lead for water pipes. The Latin word plumbum gives us our word plumbing. Lead is toxic, though. It is conjectured that lead in drinking water contributed to the decay of the Roman Empire.

Stained glass windows in the Middle Ages were crafted from shapes of colored glass separated by strips of lead. Slightly later, movable type was cast from a lead-tin alloy and separated into rows by strips of lead called leading.

St. Michael Stained Glass Window, A. Jonathan Buhalis

Lead toxicity has caused the metal to be abandoned for some uses in modern times. Lead no longer serves as a paint base in the Western world, is not used in gasoline, and is being phased out of some other uses. Substitutes for lead are generally more expensive or less effective, so traditional lead chemicals are still found in poorer countries.

Mining and Production

Lead mine production totaled 5.4 million tonnes in 2014, with the major producers being China (54%) and Australia (13%). Galena and other lead ores are separated from surrounding rock by crushing and flotation. The sulfide is oxidized by roasting and then reduced to the metal in a blast furnace.

Lead ores also contain bismuth, silver, and other trace metals that must be removed and recovered. Lead also occurs with zinc and copper and so is produced as a byproduct of those metals. Lead is the end product of radioactive decay of uranium, radium, and thorium. Those metals therefore always contain traces of lead.

Significant amounts of lead are recovered by recycling, particularly from car batteries. The amount of recycled lead produced in 2014 in the United States amounted to 70% of consumption.

Properties and Uses

Lead is a soft and malleable metal with poor conductivity and low strength. Pure lead is silvery, but the surface rapidly oxidizes and becomes dull gray. Lead is the least expensive dense metal and so is used in weights, bullets, and radiation shielding.

The low melting point of lead (327°C) allows it to be melted and poured with very simple technology – a kitchen stove, for example.

Lead is used in lead-acid car batteries. Most other kinds of rechargeable battery are more convenient in terms of weight and size, but lead-acid can generate a very high current.

lead-acid battery, A. Jonathan Buhalis

Pewter and solder are lead-tin alloys that are being phased out in favor of safer metals.

Pewter tobacco jar from the American Revolutionary War, A. Jonathan Buhalis
(c) 2007-2016 Virtual Wall Street
Content by Jonathan Buhalis
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