Zinc Extraction

The extraction of zinc from sphalerite is a somewhat complicated process, but manageable with a minimal level of technology (probably first done in India, sometime before the 4th century BC). The first step is roasting the ore to form zinc oxide. The zinc oxide is then reduced with carbon to extract the pure zinc.


The remains of a brick furnace, similar the type of furnace that would be used to to reduce zinc oxide.

 Both steps require substantial heat, which would be generated in a forge by the burning of charcoal, perhaps with the addition of some sort of bellows apparatus. The formula for the roasting of sphalerite is 2ZnS(s) + 302(g) -> 2ZnO(s) + 2SO2(g). This process requires oxygen, so either it would be done in the open air, or some sort of bellows/fan arrangement would have to be worked out. Probably initially open air is the most practical. It would probably take about 4 hours of intense heat before the roasting process is complete. This will be indicated by a change in flame color from blue to white.
The resulting material will be placed in a chamber next to a furnace. It will be heated in the presence of the carbon monoxide resulting from the burning of fuel in the furnace. This will result in the reduction of the zinc oxide. The formula is ZnO(s) + CO(g) CO2(g) + Zn(g). The resultant zinc is a gas. It will flow down through a perforated terra-cotta plate on which the material is resting, and will condense in a cooler chamber below the furnace chamber (the condensation chamber). This is the final Zn(s) metal.

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