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