Manufacturing of the Lime and Different types of lime

Lime

Lime is not available in free state. It is produced by Calcination of Lime stone/ Dolomite. Limestone is calcium carbonate CaCO₃ while Dolomite is calcium magnesium carbonate CaMg(CO₃)₂.

[ calcination is the process of heating an ore upto the redness].

Lime

Note- Lime obtained from relatively pure lime stone (90 to 95 % purity ) is referred as quick lime or caustic lime or lump lime.

Quick lime has very high affinity (reactivity] for water, hence instantly reacts with it & undergoes slaking leading to the formation of hydrated lime , slaked lime, or milk of lime (slaking is the process in which quick lime reacts with the water & swells cracks & falls out in the powder form]

Slake lime must be used as fresh as possible as it has very high affinity for CO₂ hence, instantly reacts with it & PPt out in the form of calcium carbonate.

CaCo₃→ Cao (quick lime or caustic lime or lump lime) + Co₂↑

Cao + H₂O → Ca(OH)₂ (hydrated lime, slaked lime, or milk of lime ) + Heat [15.6 kcal/gm] ]

Ca(OH)₂+ CO₂ → CaCO₃ ↓

Constituents of lime-

1- Clay-

Clay imparts hydraulicity [ it is the property of lime by the virtue of which it is able to set in water, damp locations & in thick retaining wall where there is no free circulation of air] to the lime & makes it insoluble in water.

If it is in excess, it arrest the slacking & if it is in deficiency it retards the slacking. For good lime clay proportion should be in the range of 8 to 30 %.

2- Soluble silica –

Silicates of calcium , magnesium & aluminum are also responsible for hydraulicity in lime.

3- Magnesium carbonate–

Carbonate of magnesium in lime allows it to slake & set slowly. If its concentration is more than 30% , it also imparts hydraulicity to the lime even in the absence of clay. It is also responsible for development of strength in it.

Different types of lime-

1- Fat lime-

This lime slakes vigorously due to which its volume increases by 2 to 2.5 times more than its original volume. Hence it is referred as Fat lime. It possess perfect white colour, hence it also termed as white lime.

It is obtained by the calcination of Lime stone of approximately 95 % of purity. Hence is also referred as Pure lime, rich lime or highly caustic lime.

This lime shows-

More plasticity.
Slow setting.
Solubility in water.
Perfect white color.

Hence it find its application in Engg. Work whaere aesthetic importance is more.

Example- Whitewashing, Plastering.

2- Hydraulic lime-

It is also referred as water lime as it is capable of setting in water & in damp locations. It is obtained by the calcination of lime stone having the purity in the range of 70 to 92% . It is insoluble in water and possess off white colour.

It hardens comparatively faster than fat lime ,hence it is used in Engg. Works where strength is required.

Example- Brick masonry, stone masonry.

3- Poor lime-

It is also referred as impure lime or lean lime as it is obtained from the calcination of the lime stone having purity less than 70%. This lime does not undergo slaking, hardens very slowly and possess muddy white colour. Hence is used in engg. Works of minor importance.

Example- Brick work around foundation.