Question

Describe the factors which are necessary to be considered before deciding on the method of extraction of a metal from its ore.

Answer 1

Before selecting the method of extraction of a metal from its ore, the following factors must be considered:

1. Nature of the ore: Whether the ore is an oxide, sulphide, carbonate or halide. 
   Example: Oxides are reduced directly, but sulphides are first roasted to oxides.
2. Reactivity of the metal: Highly reactive metals (Na, K, Ca, Al) are extracted by electrolysis. Moderately reactive metals (Zn, Fe, Pb, Cu) are extracted by chemical reduction. Less reactive metals (Au, Ag, Pt) occur native and are obtained by physical methods.
3. Thermodynamic feasibility: Extraction depends on Gibbs free energy change (ΔG). A reducing agent must have a more negative ΔG of oxide formation than the metal oxide to be reduced (Ellingham diagram).
4. Cost of the process: The method chosen should be economical and suitable on a commercial scale.