How are smelting, roasting, and leaching used to extract metals from ore?

Extractive metallurgy employs several thermal and chemical processes to isolate metals from ore. These methods are often used sequentially to convert complex minerals into forms suitable for final refinement.1

Roasting

Roasting is a pyrometallurgical process that involves heating ore in air at temperatures below its melting point. Its primary purpose is to chemically transform minerals—most commonly converting sulfide ores into oxides—while releasing sulfur as sulfur dioxide gas. This step prepares the material for further treatment by making impurities more soluble or easier to remove in subsequent stages.123

Smelting

Smelting involves heating ore or concentrate beyond its melting point, typically in the presence of reducing agents like coke or oxidizing agents. During this process, the material separates into two distinct liquid layers: molten metal and waste rock, known as slag. Fluxes, such as limestone, are often added to combine with impurities and facilitate the formation of this slag, which is then separated from the valuable metal.413

Leaching

Leaching is a hydrometallurgical process where metallic compounds are selectively dissolved from ore using an aqueous solvent, such as sulfuric acid, water, or cyanide solutions. This method can be performed via heap leaching, tank leaching, or in situ methods depending on the ore grade. Once the metal is dissolved into a pregnant solution, it is separated from the solid residue and recovered through further processing.15