Pyrometallurgy is a process through which ores and metals are heated to produce a finished product of workable compounds, purer metals and alloys. The process may be any of the following: drying, roasting, smelting, refining, and alloying, among others. By using high temperatures, one can cause chemical and exothermic reactions in materials. Various methods of heating can be performed, and these can all be referred to as pyrometallurgy. All processes use heat to change some aspect of the material being worked. The change may be as simple as heating water or other liquids to a gas state and then removing them. Or it could be as complex as chemically bonding metals, such as when copper and tin are combined to make bronze.
Drying is a type of pyrometallurgy in which moisture is removed from the material. Heat is applied to make the metal hotter than the boiling point of water, and then the moisture can be extracted from the material. Roasting is another type of pyrometallurgy. This occurs when metal sulfide is heated to a point that oxygen reacts to form solid metal oxide and sulfur dioxide gas.
Smelting is another form of pyrometallurgy which involves thermal reactions at a molten phase. Smelting typically takes place at a temperature higher than the metal’s melting point, and removes carbon dioxide from the material, leaving a more refined metal. Refining is another pyrometallurgical process which removes impurities by heating the metals.
Alloys are combinations of metals with other metals or of metals with non-metals. A common example of this is bronze, a combination of copper and tin. If one heats copper to about 2000° Fahrenheit (1100° Celsius) and adds tin, bronze can be made. Alloying is another form of pyrometallurgy.
In all types of pyrometallurgy, fuel or electricity is needed as the source of the heat. Sometimes exothermic reactions can provide enough heat for the pyrometallurgical process to take place. At this point, when no additional fuel or electricity is needed to work the metal, then the process is known to reach an autogenous phase.
Generally, pyrometallurgical processes are used on materials which tend to not be very reactive, as reactive materials may be encouraged to explode when heat is applied. Non-reactive elements may be extracted by heat and refined by using heat to apply other materials and causing impurities to bond and become easier to remove, allowing for a more pure form.
