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What Is Lime?

The word “lime” refers to products derived from burnt (calcined) limestone, such as quicklime and hydrated lime. Limestone is a naturally occurring and abundant sedimentary rock consisting of high levels of calcium and/or magnesium carbonate, and/or dolomite (calcium and magnesium carbonate), along with small amounts of other minerals. It is extracted from quarries and underground mines all over the world. 

Lime and limestone products are among the oldest materials used in a diverse range of applications. Today these products serve as an essential building block in every industrial process. 

Lime is commonly used to describe one of the following products: 

  • Calcium oxide / quicklime 
  • Calcium hydroxide / hydrated lime 
  • Ground calcium carbonate / limestone 
  • Precipitated calcium carbonate / PCC 
  • Other calcium products 


What is calcium oxide / quicklime?
Calcium oxide (CaO) or quicklime can be classified as either high calcium or dolomitic. High calcium quicklime has typically >97% CaO with magnesium oxide (MgO) levels less than 3%. At MLC, our high calcium oxide (CaO) content is a result of our 98.5% pure calcium carbonate (limestone). Dolomitic quicklime generally contains >40% MgO along with the calcium oxide. See our website under the “Products” tab to view more information.
What is calcium hydroxide / hydrated lime?
Calcium hydroxide {Ca(OH)2}, or hydrated lime, is a refined product. Calcium oxide is stoichiometrically reacted with water in a controlled process to form a calcium hydroxide product that has the consistency of a fine white powder containing less than 2% residual moisture. There are two major types of hydrated lime – Type N and Type S. Type S hydrated lime is mainly used in the building construction industry. Our hydrated lime portfolio is centered on Type N (Normal) Hydrated Lime. See our website under the “Products” tab to view more information.
What is ground calcium carbonate / limestone?
Ground calcium carbonate or limestone occurs naturally and is commonly called chalk or marble. MLC ground calcium carbonate is mined from one of the purest limestone deposits in the world with an average purity of 98.5% CaCO3. See our website under the “Products” tab to view more information.
What are other calcium products?
Other calcium products is a group of limestone derivatives co-products that have not been previously discussed. Some typical materials are hydration process tailings (Code H), lime kiln dust (Code L), and limestone screenings. See our website under the “Products” tab to view more information.
What sort of precautions should be taken in handling quicklime or hydrated lime?
Quicklime and hydrated lime should be treated as any other chemical and users should refer to Material Safety Data Sheet (MSDS) prior to use.
Where is lime typically stored?
Lime needs to be stored in silos or at a minimum under roof in dry areas. Since quicklime products are hydroscopic it can react with the moisture in the air.
What regulations exist in transporting lime?
In general, lime when transported via rail or motor is not considered hazardous. Please refer to the US DOT requirements for air shipments.