Isolation of Elements

Lesson

Part 1 — from rock to metal oxide. (Formative assessment only; not in the board exam.)

In this lesson you will

Distinguish minerals, ores, gangue and flux
Choose a method of concentration (hydraulic washing, magnetic separation, froth flotation, leaching) for a given ore
Explain calcination and roasting with equations
Outline the overall steps in extracting a metal

Concept

Minerals, ores and gangue

A mineral is a naturally occurring compound of a metal. An ore is a mineral from which the metal can be extracted profitably. The earthy impurities in an ore are the gangue. All ores are minerals, but not all minerals are ores.

Table of important ores of aluminium, iron, copper and zinc with formulas
Metal	Important ores	Formula
Aluminium	Bauxite	AlOₓ(OH)₃₋₂ₓ (0 < x < 1)
Aluminium	Kaolinite (a clay)	Al₂(OH)₄Si₂O₅
Iron	Haematite; magnetite; siderite	Fe₂O₃; Fe₃O₄; FeCO₃
Copper	Copper pyrites; malachite; cuprite	CuFeS₂; CuCO₃·Cu(OH)₂; Cu₂O
Zinc	Zinc blende; calamine; zincite	ZnS; ZnCO₃; ZnO

Concept

Concentration: hydraulic washing and magnetic separation

Removing gangue is concentration (dressing or benefaction). Hydraulic washing uses the difference in density: a stream of water washes away lighter gangue, leaving heavy ore particles (used for tin and lead ores). Magnetic separation uses magnetic properties: a magnetic ore (magnetite, Fe₃O₄; chromite) is attracted to a magnetic roller and falls separately from non-magnetic gangue.

Table of concentration methods, the property each uses and examples
Method	Property used	Example
Hydraulic washing	Ore denser than gangue	Tin stone (SnO₂)
Magnetic separation	Ore or gangue is magnetic	Magnetite; wolframite from tin stone
Froth flotation	Ore wetted by oil, gangue by water	Sulphide ores (ZnS, CuFeS₂, PbS)
Leaching	Ore dissolves in a reagent, gangue does not	Bauxite in NaOH; gold in NaCN

Cookies