What is Lime?

Where does it come from?

Lime is calcium oxide.  Its chemical symbol is, CaO and atomic weight of 56.  Lime is a pozzolan compound which when mixed with water, silica and aluminum such as ordinary clay, makes a cement type material with suitable strength for road beds, grades, and sub grades.  As a chemical, it literally has 1001 uses in manufacturing.

Manufacture of Lime

Calcium oxide is made from Limestone found in high purity deposits around the world.  The limestone, calcium carbonate, mined in large chunks and ground to about 4 to 5 inches in diameter.  This ground stone then burned in high efficiency kilns at about 2100 deg. F for approximately 4 hours.  During this burning, which is called calcination, the carbon dioxide is driven off as a gas.  The hot gasses are then returned to the kiln pre-heater to heat feed stone to the kiln and improve efficiency.  After burning almost 4 hours, the limestone is converted lime, calcium oxide.  Almost half of the limestone weight is lost as the gas carbon dioxide. 

Lime Products

The lime emerging from the kiln is cooled and crushed to size, usually a pebble about 3/4 inches in diameter.  The product is then sold as is or converted to hydrated lime, calcium hydroxide by adding just the right amount of water to satisfy the chemical reaction.  This produces a dry powder calcium hydroxide having less than 2% free moisture.  This hydrated lime has a molecular weight of 74 and has many applications.  The pebble lime (called quicklime) and hydrated lime can be converted to lime slurry by adding an excess of water.  This is useful where dusting during use is a problem.  The chemical reactions for limestone conversion to hydrate lime are:

CaCO3 (limestone) + Heat (2000 deg F) = CaO (quicklime) + CO2 gas

CaO + H2O (water) = Ca(OH)2 (hydrated lime)

Lime Uses

The uses of lime are highly varied in chemical plants, agriculture, steel industry, and construction.  It is used in the steel industry as a flux in removing impurities in the melt, in industry for acid neutralization or waste treatment, in agriculture for sweetening acid soils, in municipal wastes for pasteurization of fertilizer, in construction for stabilization of soils.  Some of these uses are more detailed in the categories covered in the website.