Extraction of Metals & Metallurgy

Natural Occurrence and Extraction of Metals

Noble metals (Ag, Au, Bi, Cu, Pd, Pt) exist in nature in a free state, while more active metals (alkali and alkaline earth metals) exist in combined states like carbonates, halides, oxides, phosphates, silicates, sulphides, and sulphates.

Minerals and Ores

  • Minerals: Constituents of the earth's crust containing metals or their compounds (e.g., halite (NaCl) for sodium, sylvite (KCl) for potassium, magnesite (MgCO3) for magnesium, limestone (CaCO₂) for calcium).

  • Ores: Minerals from which metals can be profitably extracted; contain impurities called gangue.

Metallurgy

Metallurgy is the science and technology of extracting metals from ores and compounding alloys. The steps are:

  1. Preparation (Concentration) of the Ore: Examples include oil floatation and magnetic separation.

  2. Production of the Metal: Examples include roasting and calcination.

  3. Purification of the Metal: Examples include chemical reduction and electrolytic reduction.

Extraction of Active Metals

Very active metals (K, Na, Ca, Mg) are extracted from their compounds via electrolysis due to the lack of economic reducing agents.

Alloys

Alloys are mixtures of two or more metals. Alloying metals increases hardness and tensile strength, decreases ductility and electrical conductivity. Example: Copper alloys (brass, bronze), fuse metal (solder).

Gold Alloys

Gold is often alloyed with copper and silver. The purity of gold is measured in carats. Pure gold is 24 carat. 20K gold contains 20/24 parts by mass of gold.