Amalgam Process metallurgy. Before a metal can be extracted, the ore must be purified, or dressed. This involves removing as much of the gangue as possible. This is generally done by crushing the ore-bearing rock and then passing it through wire screens to separate large particles. The next step depends on the quality of the ore and on the type of metal being mined.
Some iron ore is so pure it needs little dressing.
Lower-quality iron ores undergo magnetic separation, in which ore particles pass by magnets and collect around them, leaving nonmagnetic gangue behind. Other ores are separated by flotation. In this process minerals in water stick to a froth of bubbles at the surface while the gangue sinks. This is the most widely used separation process. In the gravity separation process heavier particles in water settle faster than lighter, less dense ones.