Extraction of metals

carbon reduction

carbon (as coke/charcoal) is cheap

acts as reducing agent

displacement/reduction using a more reactive metal

expensive (you first have to extract the more reactive metal)

extraction of iron

iron oxides are reduced to iron by heating with carbon in the form of coke

coke is cheap

coke acts as a reducing agent + heat source

most common iron ore is haematite (Fe₂O₃)

iron extraction steps

iron, coke and limestone are poured in at the top

hot air is blasted into the furnace

coke burns in the hot air to form carbon dioxide

strongly exothermic

the reaction is the main source of heat

C + O₂ → CO₂

carbon dioxide reacts with carbon to form carbon monoxide

C + CO₂ → 2CO

the carbon monoxide is the main reducing agent

carbon monoxide reduces the iron in the iron ore

3CO(g) + Fe₂O₃(s) → 2Fe(l) + 3CO₂(g)

carbon also reduces the iron

3C(g) + Fe₂O₃(s) → 2Fe(l) + 3CO₂(g)

the heat decomposes the limestone to give calcium oxide

the impurities in iron oxide (silicon dioxide) reacts with calcium oxide to give slag

the rocky impurities don't melt at the high temperatures

CaCO₃ → CaO + CO₂

endothermic (absorbs heat)

slag = calcium silicate

forms a layer on top of the molten iron

used in road making

the molten iron collected can be used as cast iron

very impure (contains ~4% carbon)

makes it hard and brittle

used for railings, storage tanks, cast iron pipes, water valves and pump bodies, guttering and drainpipes etc.

most of the molten iron is used to make steel

environmental problems...

loss of landscape due to size of chemical plant

noise

atmospheric pollution

disposal of slag

transport of finished iron

carbon dioxide (greenhouse effect)

carbon monoxide (poisonous)

sulphur dioxide from sulphur impurities (poisonous, acid rain)

metal oxide is reduced, carbon is oxidised

only works with metals lower than carbon in the reactivity series

because carbon can displace the metal

redox reaction

extraction of copper

mostly occurs as sulfide ores, which are heated in air to convert them to copper(II) oxide

molten copper can be produced from copper oxide by heating with carbon

copper oxide + carbon → copper + carbon dioxide

2CuO(s) + C(s) → 2Cu(l) + CO2(g)

copper oxide is reduced as carbon is oxidised ← redox reaction

unreactive metals (e.g gold) is found as the metal itself, but some reactions may be needed to remove other elements contaminating it

CaO(s) + SiO₂(s) --> CaSiO₃(l)

slag is less dense

more reactive than iron

thermal decomposition