Smelting

Chemical Reduction , or smelting, is a form of Extractive Metallurgy . The main use of smelting is to produce a metal from its ore. This applies Iron and Steel from iron Ore or to Extract Copper and other base Metal s from their Ore s.

It makes use of a chemical reducing agent, commonly a fuel that is a source of Carbon such as Coke , or in earlier times Charcoal , to change the Oxidation State of the metal ore. The carbon or Carbon Monoxide derived from it removes Oxygen from the ore to leave the metal. The carbon is oxidised, producing Carbon Dioxide and Carbon Monoxide . As most ores are impure, it is often necessary to use Flux , such as Limestone is used to remove the accompanying rock Gangue as Slag (also called Scoria or Cinder ).

EARLY IRON SMELTING

The earliest evidence to date for the ). However, based on the archaeological record of iron artefacts, it is clear that intentional reduction of iron metal from terrestrial ores (in the case of Hammeh a Haematite ore), must have started near the end of the Late Bronze Age (ca. 1600–1150 BC). Where and how iron smelting was discovered is widely debated, and remains uncertain due to the significant lack of production finds. Nevertheless, there is some consensus that iron technology originates in the Near East, perhaps in Eastern Anatolia .

In Ancient Egypt somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC) there are indications of iron working. Significantly though, no evidence for the smelting of iron from ore has been attested in Egypt in any period. There are further indications of iron smelting and working in West Africa in 500 BC {Link without Title} .

Most early processes in Europe and Africa involved smelting iron ore in a Bloomery , where the temperature is kept low enough so that the iron does not melt. This produces a spongy mass of iron (called a bloom, which then has to be consoldated with a hammer.

LATER IRON SMELTING

From the medieval period, the process of direct reduction in bloomeries began to be replaced by an indirect process. In this a Blast Furnace was used to make Pig Iron , which then had to undergo a further process to make forgeable bar iron. Further details of this will be found in the article on the Blast Furnace . Processes for the second stage include fining in a Finery Forge and from the Industrial Revolution Puddling . However both processes are now obsolete, and wrought iron is now hardly made. Instead, mild Steel is produced from a Bessemer Converter or by other means.

BASE METALS

The ores of base metals are often sulphides. In recent centuries, containing most of the impurity elements, and the other a sulfide "matte" containing the valuable metal sulfide and some impurities. Such "reverb" Furnace s are today about 40m long, 3m high and 10m wide. Fuel is burned at one end and the heat melts the dry sulfide concentrates (usually after partial roasting), which is fed through the openings in the roof of the furnace. The slag floats on top of the heavier matte, and is removed and discarded or recycled. The sulfide matte is then sent to the Converter . However the precise details of the process will vary for one metal to another.

SEE ALSO

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Smelting