Fire refines by using heat and often oxygen to selectively remove impurities from a substance, particularly metals.
Fire refining is a metallurgical process used to purify crude metals. The core principle involves leveraging high temperatures (fire) to facilitate chemical reactions that separate desired metals from unwanted elements.
The Process: Selective Oxidation
According to the provided reference, metals like iron, copper, and lead are refined through a process called selective oxidation. This method relies on the difference in how easily the metal and its impurities react with oxygen at elevated temperatures.
Here's how selective oxidation works in fire refining:
- Heating the Metal: The impure metal is first melted in a furnace.
- Adding Oxygen/Air: Oxygen or air is then introduced into the liquid metal.
- Preferential Oxidation of Impurities: Impurities present in the metal have a stronger affinity for oxygen than the base metal itself under these conditions. This means they react with the added oxygen first.
- Formation of Oxides: The impurities transform into metal oxides.
- Removal of Oxides: These impurity oxides are then removed. They can either:
- Form a slag, which is a molten layer that floats on top of the denser liquid metal and can be skimmed off.
- Become volatile oxide gas that escapes from the furnace.
This selective reaction allows the impurities to be removed while leaving the desired metal in a purer state.
Examples of Fire-Refined Metals
As noted in the reference, metals commonly refined using this fire-refining technique include:
- Iron
- Copper
- Lead
In each case, specific impurities are targeted based on their chemical properties and reaction rates with oxygen at the refining temperature.
Outcome of Fire Refining
The result of fire refining is a metal with significantly reduced levels of impurities, making it suitable for various industrial applications that require higher purity. While it may not always achieve the highest purity levels compared to other refining methods (like electrolytic refining), fire refining is often an essential step or sufficient for many purposes.
