reduce
To produce metal from ore by removing nonmetallic elements in a smelter.
reduce: strip ore down to pure metal
In metallurgy, to reduce means to remove oxygen or other nonmetallic elements from ore, leaving behind the metal itself. This is the core job of the smelter: the ore arrives as a chemical compound (usually an oxide, sulfide, or carbonate), and reduction breaks that compound apart so the metal can be collected. Without reduction, you have rock; with it, you have metal.
The most common reducing agent is carbon monoxide, produced by burning coke in a blast furnace or similar vessel. As hot CO gas passes through the ore bed, it reacts with oxygen atoms in the mineral, forming CO2 and releasing the metal. Iron oxide becomes iron; copper oxide becomes copper. Other reducing agents include hydrogen (used in some modern processes), aluminum (in thermite reactions), and carbon itself, depending on the ore and the metal being extracted.
Temperature and atmosphere matter
Reduction is not a gentle process. Iron is typically reduced at temperatures above 1200 degrees Celsius. The furnace must maintain a reducing atmosphere, meaning a low-oxygen environment; if oxygen is present, the metal will reoxidize instead of staying pure. This is why control of gas flow, coke ratio, and temperature in the furnace is critical to yield. Poor reduction leaves metal locked in slag or produces impure metal that must be refined further.
The term comes from the Latin reducere, meaning to lead back or restore. Historically, chemists thought of reduction as restoring the metal to its original state. The word stuck even though modern chemistry defines reduction more broadly as the gain of electrons. In the smelter floor, the old meaning is still the one that matters: you are reducing ore to metal.
Reduction is distinct from refining. Reduction extracts the metal from its ore compound; refining removes impurities from the metal itself. A blast furnace reduces iron ore to produce pig iron, which is then refined in a converter or furnace to make steel. Many nonferrous metals also require a refining step after reduction to reach commercial purity.