electrochemical principles of metallurgy

GENERAL PRINCIPLES AND PROCESSES OF ISOLATION OF ELEMENTS

ELECTROCHEMICAL PRINCIPLES OF METALLURGY

APPLICATIONS

EXTRACTION OF METALS AND NON METALS BY

OXIDATION AND REDUCTION

Like application of thermodynamic principles in pyrometallurgy, electrochemical principles are applied in the reduction of metal ions in solution where they are reduced by electrolysis or by adding some reducing elements.

For any reduction to occur,  must be –ve but the of more reactive metals are more -ve which makes  positive, hence their reduction is difficult. So, we take the difference of two  values corresponding to positive   then the less reactive metal comes out and more reactive metal goes to the solution. For example,

In simple electrolysis, the  ions are discharged at the cathode or negative electrode and deposited there. Depending on the reactivity of the metal produced, the materials of the electrodes are selected. Sometimes, addition of flux makes the molted mass more conducting. Used for the extraction of metals. Eg. Na, Mg, Al, etc.

Application of Electrolysis to MetallurgyElectrometallurgy is the process of extraction of metals by electrolysis of their fused salts where electrons serve as reducing agent.(a)Electrolytic reduction (Hall-Heroult process): Purified  is mixed with  which lowers its melting point of mixture and brings electrical conductivity. Fused mixture is electrolyzed using number of graphite rods as anode and carbon lining as cathode.The process of obtaining aluminium by electrolysis of a mixture of purified alumina and cryolite is known as Hall and Heroult process.

(b) Copper from low grade ores and scraps: Copper is extracted by hydrometallurgy.•Hydrometallurgy is the extraction of metals by dissolving the ore in a suitable reagent followed by the displacement of the metal by a more reactive one.

•Leaching : Low grade copper ores and scraps are leached by using acid or bacteria.

•Reduction : The solution containing   is treated with scrap iron or 

EXTRACTION OF NON METALS BY OXIDATION

ISOLATION OF CHLORINE

= +422 kJ

The reaction requires an external e.m.f. in excess of 2.2 V to overcome some other hindering reactions. Thus, Cl2 is obtained by electrolysis giving out H2 & aqueous NaOH as by products.

EXTRACTION OF GOLD AND SILVER

Involves leaching of metals present in the ore with CN- ions. This is also an oxidation reaction as Au is oxidized to Au+ which

then combines with CN- ions .

EXTRACTION OF METALS BY OXIDATION AND REDUCTION

The metals can be recovered by reduction using electropositive zinc metal.

Here zinc acts as the reducing agent.