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,
Tinstone (Cassiterite) Cr2O3
Cuprite (Rubby copper) Cu2O
Lime stone CaCO3
Chile saltpeter NaNO3
Salt petre KNO3
Epsom salt MgSO4.7H2O
Glauber’s salt Na2SO4.10H2O
Phosphates and Silicates
Lepidolite (Li, Na, K)2Al2(SiO3)(F,OH)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.