Metallurgy - Ores and minerals

 Metals occur in nature sometimes in free or native state, but most of these occur in nature in the form of chemical combination, i.e., in the form of their stable compounds which are associated with gangue or matrix. The earthy impurities such as sand, clay, rocks etc. associated with ore are collectively known as gangue or matrix. Thus a large number of metals in nature occur in the combined form along with other elements, but some metals, such as Ag, Au, Pt etc. occur in the native form (metallic state) in some regions. Ag occurs in native (or free) as well as in the form of compounds. The natural material in which the metal or their compounds occur in the earth is known as mineral. Thus a mineral is a naturally occurring material present in earth's crust which contains metal in the native (or free state) or in combined state.

 A mineral may be a single compound or a complex mixture of various compounds. When a mineral contains sufficient amount of a metal in combined state, from which it can be readily and profitably separated on commercial scale, then the mineral is said to be an ore of the metal. Thus all ores are minerals, but all minerals are not ores. A mineral from which a metal can be profitably extracted is called an ore. For example, clay (Al₂O₃ 2 SiO₂ 2 H₂O) and bauxite (Al₂ O₃ 2H₂O) are two minerals of aluminium, but aluminium, can be profitably extracted only from bauxite and not from the clay. Hence bauxite is an ore of aluminium, while clay is a mineral. The biggest source of metal is the earth's crust and the process of taking out the ores from the earth crust is called mining.

 In the combined state ores are generally found in the form of oxides, sulphides, carbonates, sulphates, chlorides and silicates.

Ore   Ore or                  Composition        Metal

          Mineral                         Present

Oxide ores

               Bauxite           Al2O3 .2H2O       Al

          Cuprite                 Cu2O          Cu

          Haematite             Fe2O3         Fe

          Zincite                  ZnO   Zn              

          Tinstone     or      SnO2 Sn

          Casseterite           

          Pyrolusite   MnO2         Mn

          Pitch Blende         U3O8          U

Sulphide ores

               Copper           Cu2S, Fe2S3 or Cu2S . FeS2  Cu

          Pyrites                          

          Copper                 Cu2S Cu

          Glance                           

          Zinc Blende ZnS   Zn

          Cinnabar              HgS   Hg

          Galena                  PbS   Pb

          Argentite     or      Ag2S Ag

          Silver                   

          Glance                           

Carbonate ores

          Magnesite             MgCO3       Mg

          Dolomite              CaCO3.MgCO3   Mg

          Calamine              ZnCO3        Zn

          Malachite             CuCO3.Cu(OH)2 Cu

          Limestone             CaCO3       Ca

Halide ores

          Rock Salt    NaCl Na              

          Carnallite    KCl.MgCl2.6H2O          Mg

          Horn Silver AgCl Ag

          Sylvine       KCl   K

          Cryolite      3 NaF.AlF3 or Na3AlF6         Al

Sulphate ores

          Epsom Salt MgSO4.7H2O      Mg

          Gypsum      CaSO4.2H2O       Ca

          Barytes       BaSO4        Ba

          Anglesite     PbSO4        Pb

Silicate ores

          Asbestos     CaSiO3.3MgSiO3          Mg             

          Felspar       K2O.Al2O3.6SiO2 or    Al

                   KAlSi3O8  

          Mica  K2O.3Al2O3.6SiO22H2O      Al

Phosphate ores

          Phosphorite          Ca3(PO4)2 P