Principles Of Extraction Of Metals :

All the materials found in the earth are composed of elements. There are about 112 elements known which constitute the entire matter on the earth. Therefore, the elements are regarded as the building blocks of the universe. These 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 elements. The elements have been broadly divided into metals and non-metals on the basis of their physical and chemical properties.

Occurrence of Metals

Element which have low chemical reactivity generally occur native or free or metallic state. e.g. Au, Pt noble gas etc. Element which are chemically reactive, generally occur in the combined state. e.g. halogens, chalcogens etc. The natural materials in which the metals occur in the earth are called minerals. The mineral from which the metal is conveniently and economically extracted is called an ore. All the ores are minerals but all  minerals 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 earth crust may be given as,

         Al (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 contain 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. sometimes lumps of pure metals are also found. These are termed nuggets. Iron is found in free state as meteroites 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. Important ores of this group are

(iii) Oxidised ores : In these ores, metals are present as their oxides or oxysalts such as carbonates, nitrates, sulphates, phosphates, silicates, etc.

         Important ores of this group are listed below,

Oxides

Carbonates

Nitrates

Sulphates

Phosphates and Silicates

         (iv) Halide ores : Metallic halides are very few in nautre. Chlorides are most common. For example.

         Common salt NaCl;   Horn silver AgCl

         Carnallite KCl.MgCl₂.6H₂O

         The important fluoride ores are

         Fluorspar CaF₂;           Cryolite Na₃AlF₆

Example 1: Carnellite is a mineral of

         (a) Ca                            (b) Na

           (c) Mg                           (d) Zn

Ans: c

Example 2: The salt  which is least likely to be found in minerals is

         (a) Chloride                 (b) Sulphate

         (c) Sulphide                (d) Nitrate

Ans: d

Example 3: Metal which can be extracted from all the three dolomite, magnesite and carnallite is                     

       (a)   Na                        (b) K

         (c)  Mg                         (d) Ca

Ans: c