Purification is the process of separating a substance of interest from foreign or contaminating elements, and can take one or more of the following forms:
Condensation or distillation is used to remove soluble substances from liquids, which cannot be done through filtration due to the small size of the substances.
Smelting is used to produce metals from raw ore, and involves adding chemicals to the ore and heating it up to the melting point of the metal.
Refining is used primarily in the petroleum industry, whereby crude oil is heated and separated into stages according to the condensation points of the various elements.