Limekilns
Most Dorset villages and private estates once had their own limekilns, to produce lime for building mortar and especially for agricultural improvements. Lime production was introduced to Britain by the Romans and a suspected Roman limekiln was identified by excavations in 1938 at Colliton Park, Dorchester. There are also references to lime-burning from accounts of building works and repairs at Corfe Castle in the thirteenth and fourteenth centuries.
The chemical process of lime-burning (calcination) is outined below. On heating calcium carbonate (limestone or chalk) to 900 C or above, carbon dioxide is released (thermal decomposition) leaving about half its own weight of calcium oxide (lime or quicklime). At these temperatures the limestone/lime glows with the peachy colour of 'limelight'. Calcium oxide reacts violently with water (hence quicklime) to form hydrated (slaked) lime, which is much more soluble than limestone.
CaCO3 -> CaO + CO2
CaO + H2O -> Ca(OH)2
Hydrated lime, in the form of lime putty, reacts with atmospheric carbon dioxide and sets, reforming calcium carbonate.
Ca(OH)2 + CO2 -> CaCO3 + H2O
In the presents of silicate minerals, the setting reaction is more complex, does not depend on carbon dioxide, and can take place under water (hydraulic lime). Similar setting reactions occur in cement.
The chemical process of lime-burning (calcination) is outined below. On heating calcium carbonate (limestone or chalk) to 900 C or above, carbon dioxide is released (thermal decomposition) leaving about half its own weight of calcium oxide (lime or quicklime). At these temperatures the limestone/lime glows with the peachy colour of 'limelight'. Calcium oxide reacts violently with water (hence quicklime) to form hydrated (slaked) lime, which is much more soluble than limestone.
CaCO3 -> CaO + CO2
CaO + H2O -> Ca(OH)2
Hydrated lime, in the form of lime putty, reacts with atmospheric carbon dioxide and sets, reforming calcium carbonate.
Ca(OH)2 + CO2 -> CaCO3 + H2O
In the presents of silicate minerals, the setting reaction is more complex, does not depend on carbon dioxide, and can take place under water (hydraulic lime). Similar setting reactions occur in cement.
