Extraction of Metals

Chemistry Metals & Non-Metals Extraction of Metals  OCCURENCE OF METALS IN NATURE: A metal is said to occur native or free when it is found in nature in the metallic state. Those metals which remain unaffected by moisture, oxygen and carbon dioxide of the air can occur native or free. The reactive metals, i.e., the metals which react with moisture, oxygen, carbon dioxide or other chemical reagents, are not found in nature in free state, but in combined state in the form of compounds. Occurrence of metals in nature In free state In combined state (gold, platinum, silver, mercury, etc.) (sodium, calcium, potassium, aluminum, lead, copper, etc).  MINERALS AND ORES Minerals: Metal-bearing substances, found in the earths crust, are called minerals. In other words, the solid compounds of metals occurring in nature are called minerals. Metals can also be classified in terms of their nature and behaviour. For example, metals resembling iron in properties like manganese, chromium, nickel are ferrous metals. They have a similar magnetic behaviour like iron and can be used for preparing magnets. Ores: The minerals from which metals can be obtained on a commercial scale are called ores. In other words, the minerals from which metals can be extracted profitably are called ores. 1 Chemistry For example, Earth’s crust contains aluminium in the form of two well-known minerals bauxite (Al2O3 . 2H2O) and china clay (Al2O3, 2SiO2 . 2H2O). But the extraction of aluminium is cheaper and easier from bauxite. Hence, ore of aluminium is bauxite. Thus it can be concluded that – (i) All ores are minerals, but all minerals are not ores. (ii) An ore is rich in the amount of the metal. The amount of foreign materials or impurities is low in an ore. Flux : A flux is a substance that is added to the furnace charge (roasted or calcined ore and coke) during the process of smelting to remove the nonfusible impurities present in the ore. 2 Chemistry Slag : Flux combines with the nonfusible impurities to convert them into a fusible substance known as slag. Impurities present in metal oxides may be acidic or basic. For acidic impurities, such as SiO2 or P2O5, a basic flux (e.g., CaO) is added to the mixture during smelting. If basic impurities such as MnO are present, silica is added to the flux. Impurity Flux Slag SiO2 CaO — CaSiO3 + P2O5 + MnO + 3CaO — Ca3(PO4)2 SiO2 — MnSiO3. Gangue or Matrix: The ore mined from the earth’s crust contains some unwanted substances or impurities, such as sand, rocky or clay materials. These substances are called gangue or matrix. 3 Chemistry Aluminium is the most abundant metal in the earth’s crust. All minerals of a metal cannot be used for extraction of the metal. USES OF METALS Metals are used in the form of pure metals, alloys and in the form of metal compounds. USE OF PURE METALS  Zinc: (i) It is used to galvanise iron to prevent it from rusting. (ii) It is used in making alloys such as brass and bronze.  Iron: It is used as a catalyst in the manufacture of ammonia by the Haber’s Process.  Mercury: It is used in preparing amalgams.  Silver and Gold: (i) Both are used in making ornaments and jewellary. (ii) Both are used in making coins.  Chromium and Nickel: (i) Both these metals are used in electroplating, cycle, motorcycle and other automobile parts. (ii) They are mixed with other metals to prepare useful alloys.  Titanium: Titanium is a light metal. It has a high melting point and boiling point. It is highly resistant to corrosion and has a high tensile strength, even higher than that of steel. Due to these properties, it has the following uses : (i) Preparing steel for defence installations (military hardware) marine instruments, aircraft frames. Hence referred to as a ‘strategic element’. (ii) Titanium is used in nuclear reaction. (iii) Titanium is used for making strong structures for construction of buildings. 4 Chemistry SOME IMPORTANT METALS COMPOUNDS USED IN DAILY LIFE:  Silver Nitrate (AgNO3) : It is also known as lunar caustic It is colourless, transparent, crystalline solid and soluble in water. Uses : (i) As laboratory reagent, (ii) In preparation of marking inks, (iii) In photography  (iv) In silvering of mirror, (v) In manufacturing of other salts of silver. Silver Bromide (AgBr): It is pale yellow coloured crystalline compound, insoluble in water. Uses : In photography  Potash Alum : (K2SO4. Al2(SO4)3 24H2O) Potash alum is a double salt of aluminum sulphate and potassium sulphate. It is soluble in water. In potash alum crystalline water is found in large amount, so on heating it expands in volume. Uses: In softening of water.  Blue Vitrol or copper sulphate (CuSO4.5H2O) : Copper sulphate is also known as blue vitrol. It is blue coloured, crystalline substance. On heating it gradually releases the crystalline water  CuSO4.H2O  CuSO4  CuO + SO2 CuSO4.5H2O  373 K 413K Uses : (i) In electroplating (ii) In electric batteries. 5 443K Chemistry (iii) The mixture of CuSO4 and lime is known as bordeaux mixture, it is used as fungicide, (iv) In dyeing of clothes , (v) In preservation of wood 6