The different types of methods used for the concentration of ores separate the impurities from the ore. However, the gangue is not completely separated and still remain in the ore. To remove all the gangue, certain types of compounds are added to the system. These compounds combine with the gangue and form light easily fusible material, which is insoluble in molten material. Such compounds are known as flux, and the fusible material formed is known as slag. The slag formed is lighter, and could be easily removed from the surface of the fused metal. Slag also helps in preventing the oxidation of the metal.

In the process of metallurgy, the ores are first powdered and then concentrated for extraction of the metals. The method used for concentration of ores depends on the nature of the ore and the impurities associated with it. These methods also include processes such as leaching. The leaching process is used for concentration of ores that are soluble in some suitable solvent. The ore is treated with a reagent that dissolves the ore but not the impurities. Leaching is carried out for ores of aluminium (bauxite), silver and gold.

In the process of metallurgy, the ores used are first crushed and powdered, and then concentrated by various methods. Following the concentration, the metal is now extracted from the ore. To achieve this, the ore is first converted into a compound which is easy to reduce. This is achieved by various methods including calcination. Calcination is a process of converting an ore into its metal oxide, by heating the ore in limited supply or absence of air, at a temperature which is just below its melting point. In this process, the moisture is removed, the volatile impurities get expelled, and the carbonate ores are converted into oxide ores since they are easy to reduce.