Isolation of Elements: Principles and Processes

Mineral and Ore

Definition and Classification

Minerals are naturally occurring chemical compounds found in the earth's crust. Ores are minerals from which metals can be economically and conveniently extracted. Ores are classified based on the type of chemical compound present.

• Native ores: Metals found in their elemental form. Example: Ag, Au, Pt

• Oxidised ores: Ores containing oxides of metals. Example: Fe2O3, Fe3O4, Al2O3

• Sulphide ores: Ores containing sulphides of metals. Example: ZnS, Cu2S, CuFeS2

• Halide ores: Ores containing halides of metals. Example: NaCl, MgCl2

Type of Ore	Examples
Native	Ag, Au, Pt
Oxidised	Fe2O3, Fe3O4, Al2O3
Sulphide	ZnS, Cu2S, CuFeS2
Halide	NaCl, MgCl2

Some Important Ores of Metals

Major Metal Ores

Different metals are extracted from specific ores. The following table lists important ores for selected metals:

Metal	Ore
Aluminium	Bauxite (Al2O3·2H2O), Kaolinite (Al2Si2O5(OH)4), Cryolite (Na3AlF6), Haematite (Fe2O3), Magnetite (Fe3O4), Iron pyrite (FeS2)
Copper	Copper pyrite (CuFeS2), Chalcopyrite, Malachite (CuCO3·Cu(OH)2), Chalcocite (Cu2S)
Zinc	Zinc blend (ZnS), Calamine (ZnCO3), Zincite (ZnO)
Lead	Galena (PbS)
Mercury	Cinnabar (HgS)

Metallurgy

Overview of Metallurgical Processes

Metallurgy is the scientific and technological process used for the isolation of metals from their ores. The main steps include crushing, concentration, isolation, and refining.

• Crushing: Breaking down ore into smaller pieces.

• Concentration (Dressing): Removal of unwanted materials (gangue) to increase the percentage of metal in the ore.

• Isolation: Converting the ore to metal through reduction or other chemical processes.

• Refining: Purification of the extracted metal.

Gangue: Earthy, unwanted materials that contaminate the ore.

Flux and Slag

Flux is a substance added during smelting to combine with impurities and form a fusible product called slag. Slag is less dense than molten metal and floats on its surface, protecting it from oxidation.

Type of Flux	Example	Impurity	Slag Formed
Acidic Flux	SiO2, P2O5	Basic impurity	SiO2 + CaO → CaSiO3
Basic Flux	CaO, MgO	Acidic impurity	CaO + SiO2 → CaSiO3

General equation:

$\text{Ore} + \text{Impurity} + \text{Flux} \rightarrow \text{Ore} + \text{Slag}$

Concentration of Ores

Hydraulic Washing

This method separates ore particles from gangue based on differences in their densities. The heavier ore particles settle at the bottom, while lighter gangue particles are washed away.

• Principle: Difference in gravities of ore and gangue particles.

• Application: Used for ores like tin stone (SnO2).

Magnetic Separation

This method exploits differences in magnetic properties between ore and gangue. A magnetic separator consists of a belt that moves over rollers, one of which is magnetic. Magnetic ore particles are attracted to the magnetic roller, while non-magnetic gangue falls away.

• Example: Separation of magnetite (Fe3O4) from silica (SiO2).

• Other examples: Wolframite (FeWO4, MnWO4) from tin stone (SnO2).

Froth Flotation Process

Principle and Application

The Froth Flotation Process is used to remove gangue from sulphide ores. A suspension of powdered ore is made with water, and collectors and froth stabilizers are added. Sulphide ore particles are wetted by oil and float in the froth, while gangue is wetted by water and sinks.

• Collectors: Enhance non-wettability of ore in water (e.g., pine oil, xanthates).

• Froth stabilizers: Stabilize the froth (e.g., cresol, aniline).

• Depressants: Used to selectively separate ores (e.g., NaCN, NaCO3).

Example: Separation of PbS (galena) from ZnS (zinc blende) using NaCN as a depressant.

Selected Questions and Answers

Common Sulphide Ores

• Lead (Pb): Galena (PbS)

• Silver (Ag): Argentite (Ag2S)

• Aluminium (Al): Bauxite (Al2O3·2H2O)

• Magnesium (Mg): Found in halide ores

Matching Ores and Types

Type of Ore	Example
Carbonate	Calamine
Sulphide	Argentite
Hydroxide	Bauxite
Oxide	Magnetite

Key Terms and Concepts

• Ore: Mineral from which metal can be extracted profitably.

• Gangue: Unwanted material in the ore.

• Flux: Substance added to combine with impurities to form slag.

• Slag: Fusible product formed from flux and impurities.

• Concentration: Process of removing gangue from ore.

• Metallurgy: Science of extracting metals from their ores.

Summary Table: Types of Ore and Extraction Methods

Ore Type	Extraction Method	Example
Oxide	Reduction (smelting)	Haematite (Fe2O3)
Sulphide	Froth flotation, roasting	Galena (PbS), Zinc blende (ZnS)
Carbonate	Calcination	Calamine (ZnCO3)
Halide	Electrolysis	NaCl

Additional info: The notes also briefly mention the historical development of the Froth Flotation Process and its economic impact on copper mining, as well as the importance of scientific observation in technological innovation.