© AS 080 10-Jul-12. ORES Most metals are found in compounds in the Earth’s crust. A rock...

© www.chemsheets.co.uk AS 080 10-Jul-12

ORES

• Most metals are found in compounds in the Earth’s crust.

• A rock containing enough of the metal for extraction to be profitable is called an ore.

iron ore haematite

Fe2O3

copper ore malchite

CuCO3

titanium ore rutileTiO2

aluminium ore

bauxiteAl2O3

lead ore galena

PbS

EARTH’S CRUST

Metals have to be extracted by chemical

reactions from compounds found in the

crust.

EXTRACTION METHODS

Methods

1) Reduction by heating with carbon

2) Reduction by electrolysis of melt

3) Reduction by active metal

Which method is used depends on

1) Energy requirements (heat, electricity)

2) Cost of reductants (C / active metal / electricity)

3) Purity of metal required

4) Reduction by hydrogen

© www.chemsheets.co.uk AS 080 10-Jul-12

ROASTING SULPHIDE ORES

Ore is roasted in air

e.g. ZnS + 3/2 O2 ZnO + SO2

Produces SO2 – causes acid rain

To prevent this, SO2 is collected to stop it entering the atmosphere (and then used to make some H2SO4)

© www.chemsheets.co.uk AS 080 10-Jul-12

ACID RAINDamages plants

Branches from a tree in Germany's Black Forest show needle loss and yellowed boughs caused by acid rain

Kills fish

Damages some stones (e.g. limestone)

REDUCTION WITH CARBON

Most metals can be extracted by heating with carbon. Many are not because:

1) Metal carbides may be formed (e.g. with Ti, W, Al)

2) Temperature required is excessively high (energy costs)

© www.chemsheets.co.uk AS 080 10-Jul-12

BLAST FURNACE

1) C + O2 → CO2

2) C + CO2 → 2 CO

3) Fe2O3 + 3 CO → 2 Fe + 3 CO2

Fe2O3 + 3 C → 2 Fe + 3 CO

4) CaCO3 → CaO + CO2

5) CaO + SiO2 → CaSiO3

BLAST FURNACE

Pollution issues

1) CO2 formed – greenhouse gas

2) CO formed – toxic

3) SO2 formed (roasting of sulphide ores) – acid rain

© www.chemsheets.co.uk AS 080 10-Jul-12

STEEL MAKING

Impurities: C, P, S, Si

1) Inject powdered Mg to remove S (forms MgS – floats on surface and scraped off)

2) Scrap steel added to recycle

3) O2 blown through molten metal (converts C, P, Si to oxides, CO2 bubbles off)

4) Limestone added (decomposes to CaO) which reacts with P4O10 and SiO2 to form slag

5) Other metals and/or C added to make steel

© www.chemsheets.co.uk AS 046 10-Jul-12

REDUCTION WITH CARBON

Mn MnO2 + C Mn + CO2

Cu 2 CuO + C 2 Cu + CO2

Malachite oreCuCO3 CuO +

CO2

ELECTROLYSIS OF MELTS

graphite negative electrode

Al3+ + 3 e- Al

graphite positive electrode

2 O2- - 4 e- O2 (then C + O2 CO2)

molten mixture of aluminium oxide

and cryolite

molten aluminium

© www.chemsheets.co.uk AS 046 10-Jul-12

ACTIVE METAL REDUCTION

Titanium is

Replacement hip joints

Nuclear reactors

• Low density• Strong• Corrosion

resistant

Aircraft

ACTIVE METAL REDUCTION

• Titanium must be very pure.

• Reduction with C forms TiC which is brittle.

• Electrolysis does not make it pure enough.

© www.chemsheets.co.uk AS 080 10-Jul-12

Ti EXTRACTION

1) TiO2 + 2 Cl2 + 2 C → TiCl4 + 2 CO

2) Purify TiCl4 by fractional distillation

3) TiCl4 + 4 Na → Ti + 4 NaCl

TiCl4 + 2 Mg → Ti + 2 MgCl2

Expensive due to:

• High temperatures (high energy)

• Use of Ar

• Cost of Na/Mg (made by electrolysis)© www.chemsheets.co.uk AS 080 10-Jul-12

HYDROGEN REDUCTION

Wolframite (contains WO3) Tungsten

WO3 + 3 H2 W + 3 H2O

C reduction would form WC (tungsten carbide)

RECYCLING METALS

Advantages

• Lower energy cost

• Saves resources

• Less waste

• Less pollutants (e.g. CO2, SO2, CO)

Disadvantages

• Preventing people throwing away

• Transport cost

© www.chemsheets.co.uk AS 080 10-Jul-12

COPPER RECYCLING & EXTRACTION

1) Covert waste Cu to Cu2+(aq) – add H2SO4 or enzyme

2) Extract Cu from solution with Fe:

Cu2+(aq) + Fe(s) Cu(s) + Fe2+(aq)

Useful for recycling scrap extraction from low grade ores