Lead smelting
Concentrated lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates.
A reducing environment (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal.
The crude bullion and lead slag layers flow out of the 'furnace front' and into the 'forehearth', where the two streams are separated.
The crude lead bullion, containing significant quantities of copper will then undergo 'copper drossing'.
In this step elemental sulphur, usually in solid form is added to the molten crude lead bullion to react with the contained copper.
A "matte" layer forms in this step, containing most of the copper originating from the crude lead bullion and some other impurities as metal sulfides.
[6] The earliest known cast lead beads were thought found in the Çatalhöyük site in Anatolia (Turkey), and dated from about 6500 BC.
[7] Ancient smelting was done using loads of lead ore and charcoal in outdoor hearths and furnaces.
Greenland ice cores from 500 BCE to 300 CE show measurably elevated lead content in the atmosphere.
[8] Researchers studying an ice core from Colle Gnifetti, in the Swiss part of the Monte Rosa massif, have found that higher historical European airborne lead pollution levels are associated with changes in the monetary system from gold to silver from the year 640 CE, with the principal source likely to be the Melle mines in France.
Later airborne pollution, between the years 1170 and 1216 CE, correlates even more strongly with contemporaneous records of lead and silver production from mines in the Peak District of England, at levels similar to those seen in the Industrial Revolution.
[9][10][11] Georgius Agricola (1494–1555) presented details of lead smelting methods and facilities current in Europe in the first half of the 16th century in Book IX of his treatise on mining and metallurgy, De Re Metallica.
Methods ranged from primitive open-hearth arrangements (essentially bonfires on which lead ore was piled) to blast furnaces capable of continuous operation.
