Students can go through TS Inter 2nd Year Chemistry Notes 5th Lesson General Principles of Metallurgy will help students in revising the entire concepts quickly.
TS Inter 2nd Year Chemistry Notes 5th Lesson General Principles of Metallurgy
→ The naturally occurring chemical substances in the earth’s crust which are obtained by mining are known as minerals.
→ Very few minerals are chemically and com-mercially viable to be used as sources of extraction are known as ores.
→ Ores are usually associated with earthy materials called gangue.
→ The process of extraction and isolation of the metal from its naturally occurring com-pounds is called metallurgy.
→ Extraction involves the following major steps.
- Concentration of the ore.
- Isolation of the metal from the concentrated ore by chemical or electrochemical methods.
- Purification of the metal.
→ Removal of the gangue from the ore is known as concentration, dressing or benefaction.
→ Sulphide ores are concentrated by froth floatation process.
→ If either the ore or the gangue is a magnetic substance, magnetic separation method is used.
→ Isolation of metals from concentrated ore involves calcination or roasting and reduction.
→ Reduction of the metal oxide involves heating it with reducing agents.
C or CO or A/ or any other active metal.
→ Ellingham diagram consists of plots of ΔfG° Vs T for formation of oxides of elements.
→ Such diagrams help us in predicting the feasibility of thermal reduction of ore.
→ The criterion of feasibility is that at a given temperature, Gibbs energy of the reaction must be negative.
→ Iron obtained from Blast furnace contains 4% carbon and many impurities in smaller amounts (eg : P, S, Si, Mn). This is known as pig iron.
→ Copper is extracted from CuFeS2 FeS is oxidised to FeO and is removed as FeSiO3.
→ Bauxite is leached with NaOH which removes impurities.
→ A metal extracted by any method is usually contaminated with some impurity. For obtaining metals of high purity, the follow¬ing methods are in vogue.
→ Distillation : Useful for low boiling metals like zinc and mercury containing high boiling metals as impurities.
The extracted metal in the molten state is distilled to obtain the pure metal as distillate.
→ Liquation: Low melting metal like tin can be made to flow on a sloping surface leaving behind high melting inpurities.
→ Zone refining: Impurities are more soluble in the melt than in the solid state of the metal. As the heater moves forward the pure metal crystallises out of the melt and the impurities pass on to the adjacent molten zone. Impurities get concentrated at one end. This end is cut off.
→ Aluminium foils are used as wrappers for Chacolates.
→ Copper alloys are tougher than the metal itself. Ex : Brass (with zinc, and bronze (with tin).
→ Zinc is used for galvanising iron.
→ Cast iron is used for casting stoves, railway sleepers etc.