The leaching process is used in the extraction of substances from solids. The leaching Process describes the release of organic and inorganic contaminants or radionuclides from a solid phase into a water phase when influenced by processes such as desorption, complexation, and mineral dissolution. Using this process, the ore of metal can be concentrated by causing a chemical reaction with a reagent, leading to the ore being dissolved but the impurities remaining undissolved.
Leaching of Al2O3.2H2O (or bauxite) with a heated and concentrated solution of sodium hydroxide. In this example, the concentrated NaOH dissolves the aluminium present in the bauxite, whereas the impurities such as Fe2O3, TiO2, and SiO2, are not dissolved by the reagent. Therefore, the chemical reaction for this example can be written as:
Al2O3.2H2O + 2NaOH → 2NaAlO2 + 3H2O