GENERAL PRINCIPLES OF EXTRACTION OF METAL

All the materials found in the earth are comprosed of element. There are about 112 element known which constitute the entire matter on the earth. Therefore, the elements are regarded as the building blocks of the universe. There are distributed in all the three main parts of the earth; atmosphere and lithosphere. Among these, lithosphere constitutes the main source of most of the element. The element have been broadly divided into metals and non-metals on the basis of their physical and chemical properties.

OCCURANCE OF METAL

Element which have low chemical reactivity generally occur native or freeor metallic state. Eg. Au, Pt, noble gas etc. element which are chemically reactive, generally occur in the combined state. Eg. Halogen, chalcogens etc. the natural materials in which the metals occur in the earth are called minerals. The minerals from which the metals is conveniently and economically extracted is called an ore. All the ores are minerals but all ores cannot be ores. Ores may be divided into four groups.

1.      Metallic core (siderophile) of the earth crust contains (Mn, Fe, Co, Ni, Cu, Ru, Rb, Pd, Ag, Re, Os, Ir, Pt, Au). Entire composition of metals in the earth crust may be given as,

Au(8.3%); Ca(3.6%); Na(2.8%); K(2.6%); Mg(2.1%); Ti(0.4%); Mn(0.1%); Fe(5.1%) other metals (0.1%).

                               I.            Native ores: These ores contains metals in free state, e.g. silver, gold, platinum, mercury, copper, etc. These are found usually associated with rock or alluvial materials like clay, sand, etc. sometime lumps of pure metals are also found. These are termed nuggets. Irons is found in free state are meteorites which also have 20 to 30% nickel.

                            II.            Sulphurised and arsenical ores: these ores consist of sulphides and arsenides in simple and complex forms of metals. Some or ores are:

Metal              Name of the ore                     Compositions

Pb                    Galena                                     Pbs

Zn                    Zinc blender                            Zns

Ag                   Cinnabar                                  Hgs

Fe                    iron pyrites                              Fes2

Ni                    Kufer nickel                            NiAs

Cu                   Copper pyrites                         Cu2s

                         III.            Oxidized ores: In these ores, metals are present as their oxides or oxysalts such as carbonates, nitrates, sulphates, phosphates, silicates, etc.

Important ores of this groups are listed below,

Oxides

Haemalite                                            Fe2O3

Magnetite                                            Fe2O4

Limonite                                              Fe2O3.3H2O

Bauxite                                                            Al2O3.2H2O

Corundum                                           Al2O3

Diaspore                                              Al2O3.H2O

Chromite                                             FeO.Cr2O3

Chromeochre                                       FeO.Cr2O3

Tinstone (Cassiterite)                          Cr2O3

Chrysoberyl                                         BeO.Al2O3

Cuprite (Rubby copper)                                  Cu2O

Pyrolusite                                            MnO2

Zincite                                                 Zno

Rutile                                                  TiO2

Llmenite                                              FeO.TIO2

Carbonates

Magnesite                                            MgcO3

Lime stone                                          CaCO3

Dolomite                                             CaCO3.MgCO3

Calamine                                             ZnCO3

Malachite                                            CuCO3.Cu(OH)2

Azurite                                                            Cu(OH)2.2CuCO3

Cerussite                                             PbCO3

Siderite                                                            FeCO3

Nitrates

Chile saltpeter                                     NaNO3

Salt petre                                             KNO3

Sulphates

Epsom salt                                           MgSO4.7H2O

Barites                                                 BasO4

Gypsum                                               CaSO4.2H2O

Glauber’s salt                                      Na2SO4.10H2O

Anglesite                                             PbSO4

Schonite                                              K2SO4.MgSO4.6H2O

Polyhalite                                            K2SO4.MgSO4.CaSO$.2H2O

Phosphates and Silicates

Lepidolite                                            (Li, Na, K)2Al2(SiO3)(F,OH)2

Petalite                                                            liAl(Si2O5)2

Triphylite                                             (Li, Na)3PO4,(Fe, Mn)3(PO4)2

                         IV.            Halide ores : Metallic halides are few in nature, chlorides are most common . for example,

Comman salt NaCl.