© 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 Fe 2 O 3 copper ore malchite CuCO 3 titanium ore rutile TiO 2 aluminium ore bauxite Al 2 O 3 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 4) Reduction by hydrogen Which method is used depends on 1) Energy requirements (heat, electricity) 2) Cost of reductants (C / active metal / electricity) 3) Purity of metal required

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ROASTING SULPHIDE ORES

Ore is roasted in air e.g. ZnS + 3 / 2 O 2



ZnO + SO 2 Produces SO 2 – causes acid rain To prevent this, SO the atmosphere (and then used to make some H 2 SO 4 ) 2 is collected to stop it entering

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ACID RAIN Damages 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)

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BLAST FURNACE

1) C + O 2 → CO 2 2) C + CO 2 → 2 CO 3) Fe 2 O 3 Fe 2 O 3 + 3 CO → 2 Fe + 3 CO 2 + 3 C → 2 Fe + 3 CO 4) CaCO 3 → CaO + CO 2 5) CaO + SiO 2 → CaSiO 3

BLAST FURNACE

Pollution issues 1) 2) 3) CO 2 formed – greenhouse gas CO formed – toxic SO 2 formed (roasting of sulphide ores) – acid rain

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STEEL MAKING

Impurities: C, P, S, Si 1) 2) Inject powdered Mg to remove S (forms MgS – floats on surface and scraped off) Scrap steel added to recycle 3) 4) 5) O 2 blown through molten metal (converts C, P, Si to oxides, CO 2 bubbles off) Limestone added (decomposes to CaO) which reacts with P 4 O 10 and SiO 2 to form slag Other metals and/or C added to make steel

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Mn Cu

REDUCTION WITH CARBON

MnO 2 + C



Mn + CO 2 2 CuO + C



2 Cu + CO 2 Malachite ore CuCO 3



CuO + CO 2

ELECTROLYSIS OF MELTS

graphite

positive

electrode 2 O 2 - 4 e  O 2 (then C + O 2  CO 2 ) molten mixture of aluminium oxide and cryolite graphite

negative

electrode Al 3+ + 3 e  Al molten aluminium © www.chemsheets.co.uk AS 046 10-Jul-12

ACTIVE METAL REDUCTION

Titanium is

• Low density • Strong • Corrosion resistant Replacement hip joints Nuclear reactors 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) TiO 2 + 2 Cl 2 + 2 C → TiCl 4 + 2 CO 2) 3) Purify TiCl 4 by fractional distillation TiCl 4 TiCl 4 + 4 Na → + 2 Mg → Ti + 4 NaCl Ti + 2 MgCl 2 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 WO 3 ) Tungsten

WO 3 + 3 H 2



W + 3 H 2 O

C reduction would form WC (tungsten carbide)

RECYCLING METALS

Advantages

• Lower energy cost • Saves resources • Less waste • Less pollutants

(e.g. CO 2 , SO 2 , 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 Cu 2+ (aq) – add H 2 SO 4 or enzyme 2) Extract Cu from solution with Fe: Cu 2+ (aq) + Fe(s)



Cu(s) + Fe 2+ (aq) Useful for recycling scrap extraction from low grade ores