Lime (burnt or hydrated) is the most economical and widely used alkaline reagent in the chemical industry. It is used as a reagent in the manufacture of various calcic compounds (both minerals and organics), for pH control in many applications, to regenerate reagents, and for coagulation/flocculation of colloidal impurities. It is also used in construction, in mortars, concretes, etc.

Lime is produced by calcination of limestone (> 900°C). The calcium carbonate then dissociates to calcium oxyde (CaO), known as quicklime, and CO₂. This quicklime can be used as such or grinded. Quicklime can also be hydrated in hydrated lime (Ca(OH)₂), suitable for a whole range of other applications.