Lime and Pollution Control Systems

Lime (also called quicklime) is the common term for calcium oxide (CaO).  It’s produced commercially by high-temperature (approx. 2000 °F) calcification of limestone, where the following reduction occurs:

CaCO3 → CaO + CO2

The reaction also occurs in reverse, and the lime will slowly revert back to limestone when exposed to carbon dioxide.  Lime is very hygroscopic and reacts vigorously and exothermically with water.  When lime reacts with water, it forms calcium hydroxide, or hydrated lime by the following reaction:

CaO + H2O → Ca(OH)2

Some of the principal uses of lime are:

• Soil stabilization

Quicklime, when mixed with silicon-containing clays, undergoes an ion-exchange reaction and converts the clay to a cement-like substance.  The reaction occurs with hydrated lime, and water and lime are both consumed.

• Neutralization of acids

The pH of lime in water is about 12, making it a moderately strong base and a good agent for reduction of acidity.

• Drying up muddy sites

Lime is not considered harmful, but the dust is an irritant and thermal burns can occur on the skin due to the exothermic reaction with water.

Dust emission of quicklime and hydrated lime can occur during dry transfers, such as truck unloading or transfer of the material to a slurry mixer.