* The Activity Series of metals refers to the arrangement of metals in decreasing order of their reactivity.
* Reduction is the process in which metal oxides get reduced to metals by reducing agents like carbon, hydrogen, carbon monoxide, etc.
* Metals at the bottom of the activity series are not reactive and can be extracted by reduction.
* Metals at the top of the active series are highly reactive and can be extracted through electrolysis
The important ores of aluminium are:
* Bauxite
* Corundum
* Cryolite
The extraction of aluminium involves three steps:
* Purification of bauxite by Bayer’s process.
* Electrolytic reduction of anhydrous alumina by Hall and Herault’s process.
* Purification of impure aluminium by Hoope’s process.
Aluminium is used in the manufacture of automobile components, electric wires, and in the construction process.
The two important alloys of aluminium are:
* Duralumin
* Magnalium
* Duralumin is used in the making of aircraft parts and pressure cookers.
* Magnalium is used in the making of machined articles and cheap physical balances.
Concentration of Ores
* The branch of science and technology that deals with the isolation of metals from their ores is known as metallurgy.
* Metals found in nature in a combined state are known as minerals.
* An ore contains metal and other unwanted substances known as gangue or matrix
* The process of removing gangue from an ore is known as concentration of the ore.
* Hydraulic washing is a technique used to concentrate the ore by forcing water or another liquid into it.
* Magnetic separation is a technique used when either the ore or the impurities in it are magnetic in nature.
* Froth floatation separates the gangue particles from the ore, based on the fact that gangue is wetted by water, while mineral is wetted by oil.
* Leaching is used when an ore is soluble in a suitable solvent.
Metallurgy of Aluminium
* Bauxite is the main ore of aluminium
* The first step of the metallurgy of aluminium is concentration of the ore, and it is done by Baeyer’s process.
* In the second step’ alumina is reduced to get aluminium by Hall – Heroult’s process.
* The molten aluminium obtained after Hall-Heroult’s process 99% pure. It is purified by Hoope’s process to get 99.9% pure aluminium.
Occurrence of Metals
* Most metals are found in nature in a combined state owing to their high reactivity.
* The only metals found in Free State are Gold and Platinum.
* Aluminium constitutes about 8% and iron 5.8% by weight of the earth’s crust.
* Aluminium is the 3rd most abundant elements and Iron the 4th most abundant element by weight of the earth’s crust.
* Naturally occurring aluminium is a major component of silicates.
* Aluminium is extracted mainly from its principal ore- Bauxite.
* Iron is principally extracted from its oxide ores.
Metallurgy of Iron
* Iron does not occur in native state and is available in ores like haematite.
[Fe2O3], magnetite [Fe3O4], limonite [Fe2O3. H2O], siderite [FeCO3] and iron pyrites [feS2].
* Iron is extracted from its ores in three stages: concentration, calcinations and reduction.
* Haematite is concentration by hydraulic washing or gravity separation while magnetite is concentrated by magnetic separation.
* Calcination is the process of heating the ore to high temperatures in absence of air to remove the impurities.
* Smelting is the process of reducing an oxide with carbon in the presence of flux at a high temperature.
* Molten iron obtained from blast furnace is known as pig iron.
* Iron is greyish white solid metal.
* Iron alloys such as steel, stainless steel, nickel steel, nichrome, alnico and invar steel find many application across various industries.
Alloys
*An alloy is a homogeneous metallic solution composed of two or more elements.
* Alloys are classified according to their components into three distinct types, namely, ferrous, non- ferrous and amalgams.
* The important characteristics of an alloy are increased hardness, toughness and corrosion resistance, magnetisability, and ductility.
* The covert 24 carat gold into 22 carat gold, about 8.4% of another metal is added.
* Some common alloys are stainless steel, brass, bronze, sterling silver, alnico, duralumin and solder.
Extraction of Crude Metal
The isolation of metals from concentrated ore involves two major steps:
* Conservation of ore into its metal oxide
* Reduction of the metal oxide to the metal
* Concentration ore can be converted into its metal oxide by calcinations or roasting.
* Calcination is the process of converting an ore into oxide by heating it strongly below its melting point, either in the absence of air or in a limited supply of air.
* Roasting is the process of heating an ore in a furnace, with regular supply of air, at a temperature below the melting point of the metal.
* Ore is reduced to metal by using a suitable reducing agent. The choice of the reducing agent depends on the reactivity of the metal.
Refining Techniques and Uses of Metals
* Metals obtained by extraction contain impurities, which are removed by using various refining techniques.
* Distillation is refining a metal by evaporating it and then re- liquefying it.
* Liquation is passing molten metal over a sloping hearth so that it is separated from the solid impurities.
* In electrolytic refining, a strip of impure metal is used as the anode, a pure metal strip as the cathode, and a solution of the metal as the electrolyte. The impurities gather at the anode and the pure metal at the cathode.
* When a heated roller is passed over a impure metal rod, the impurities shift with the roller towards the right and pure metal crystallises in the left side. This technique is known as zone refining.
* In vapour phase refining, a metal is converted into its volatile compound which is then decomposed to give the pure metal.
* Refining is based on the relative adsorption of the components of a metal mixture with an adsorbent material.
* Metals have a variety of applications.
