5. Thermal metallurgy

In the early 19th century, zinc production on an industrial scale began using a thermal process. At the time, the raw material was oxidized ores, which could be reduced directly with coal to extract the metal. The rapid depletion of these ores led to a switch to blendes, and thus to an initial roasting stage to produce oxide.

The main feature of thermal zinc metallurgy is that the temperature at which the oxide is reduced by carbon or carbon monoxide is higher than the metal's boiling point. Since zinc is gaseous when formed, it is easier to separate it from the ore gangue, but the condensation kinetics of the vapors must be rapid to avoid the reverse oxidation reaction when the temperature drops.