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Extractive metallurgy is the practice of extracting metal from ore, purifying it, and recycling it.
Most metals found in the Earth's crust exist as oxide minerals. Metal-oxide compounds must be reduced to liberate the desired metal. Many metals exist as sulfide minerals. There are two methods of reduction: electrolytic and chemical.
Chemical reduction or smelting is the process of heating the ore with combustion agents and purifying agents to separate the pure metal from the waste products. A roasting process is used to extract metals from sulfide ores: in this process the ore is heated in the presence of oxygen and the sulfur is oxidised and driven off as sulfur dioxide.
Electrolytic reduction involves passing a large current through a molten metal oxide or molten metal oxide solution. This is how aluminium is electrolysed from bauxite dissolved in molten cryolite.
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