Ch.17. Ores/Minerals and Extractive Metallury - Core Points for Revision

Syllabus

Ores and minerals: Commonly occurring ores and minerals of
iron,
copper,
tin,
lead,
magnesium,
aluminium,
zinc and
silver.

Extractive metallurgy: Chemical principles and reactions only (industrial details excluded);
Carbon reduction method (iron and tin);
Self reduction method (copper and lead);
Electrolytic reduction method (magnesium and aluminium);
Cyanide process (silver and gold).



Ores and minerals of iron

Magnetite
Haematite
Limonite

Iron Pyrites
Copper Pyrites

Haematite is the principal ore.

Ores and minerals of Tin

Tin stone

Ores and minerals of Copper

Copper pyrites
Malachanite
Cuprite or ruby copper
Azurite
Copper glance

Minerals of Lead

Galena
Cerussite
Anglesite
Wulfenite
Stolzite

Minerals of Magnesium

Magnesite
Carnallite
Kiesserite
Schonite
Dolomite
Epsomite
kainite

Minerals of Alumium

Corundum
Diaspore
Bauxite

Cryolite

Feldspar, Mica, Kaolinite

Alunite or Alumstone
Turquoise
Aluminates of Magensium, Iron and Manganese

Minerals of Silver

Argentite
Pyrargarite
Proustite
Horn Silver

Minerals of Zinc
(from X book by Viraf Dalal)

Zincite
Calamine
Zinc Blende

Minerals of Gold

Mainly native gold

Nagyagite
Calaverite
Sylvanite
Krennerite




Fe
The reduction of the ore
At the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide.

It is the carbon monoxide which is the main reducing agent in the furnace.

Extraction of Tin

The ore is tin stone that contains 10% of the metal as SnO2.

SnO2 + 2C = Sn + 2CO

The moltenmetal is collected from the bottom of the blast furnace.
The metal may be purified elctrolytically

Copper

The concentrated ore is heated strongly with silicon dioxide (silica) and air or oxygen in a furnace or series of furnaces.

Electrolysis of magnesium

• Dolomite and seawater is precipitated
as insoluble magnesium hydroxide
Mg(OH)2 which is subsequently treated
with HCl to give MgCl2.
• MgCl2 is fed into electrolysis cell to
produce Mg metal at cathode and Cl2
at anode.

Conversion of the aluminium oxide into aluminium by electrolysis

The aluminium oxide is electrolysed in solution in molten cryolite, Na3AlF6. Cryolite is another aluminium ore, but is rare and expensive, and most is now made chemically.

Gold
It is now the most important and widely used process for extracting gold from ores.

The ore is first finely ground and concentrated by flotation.
To remove certain impurities, it may be roasted.
It is then mixed with a dilute solution of sodium cyanide (or potassium or calcium cyanide) while air is bubbled through it.
Soluble aurocyanide complex ion, Au(CN)-2^-1 is formed .
Silver, usually present as an impurity, also forms a similar soluble ion.