Smelting
The main other method for refining ores is with the use of heat. The process called smelting is where a metal is heated to a high temperature with the assistance of coal or coke (form of coal with carbon). In this process the goal is to get the undesirable particles to oxidize therefore removing the excess elements from the metal you wish to extract. As an example you can look at lead sulfide (PbS). This what happens when lead sulfide is reacted with coke.
PbS + O2 PbO + SO2
The lead reacts with oxygen to form lead oxide and sulfur dioxide. At
this point the smelting process is not completed because we have not successfully
isolated lead. The following reaction takes place when the lead oxide
reacts with the carbon from the coke.
PbO + C Pb + CO2
The product of this reaction is lead and carbon dioxide. Normally in smelting
the end result will include slag, which is the term for the waste produced
and a fairly pure metal substance. It is important to note that the resulting
metal will not be as pure as metals produced from chemical processing.
The benefits of smelting are that is relativly easy to preform. One method
used by the egyptians invloved digging a small pit in the ground and filling
it with ore and coal. Nearby by would be a bellows or some device to pump
air over the coal. After the ore has melted two drains are used, one to
exttract the liquid metal and the other to filter out the slag. Smelting
can only be used if you can generate enough heat so that it is near the
melting point.
Figure 4(above): refined pig iron being poured into molds