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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 abundent 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 limestoneproductsare among the oldest materials used by humans for avery diverse range of applications.Today these products serve as an essentialbuilding block inevery industrial process.


LIME CYCLE

After processing, products derived from limestonehave the unique ability toreturn to their original chemical form. The lime cycle consists offirst burning of limestone to form quicklime. Hydrated limecan then be produced by adding water to the quicklime. In the diagram below, carbon dioxide in the atmosphere or from industrial combustionprocessesreact with hydrated lime to convert it back to limestone.This cycle of sustainability is called the lime cycle.

LimestoneLIMESTONE PRODUCTS:

Limestone is the most important and abundant sedimentary rock and is formed by the compaction of the remains of coral animals and plants on the bottoms of oceans around the world. Limestone is composed of the mineral calcite (calcium carbonate) and/or the mineral dolomite (calcium and magnesium carbonate) along with small amounts of other minerals. There are three distinct types of limestone which are defined by their magnesium carbonate (MgCO3) concentrations:

  1. Dolomitic limestone consists of 35 to 46% magnesium carbonate.
  2. Magnesian limestone consists of 5 to 35% magnesium carbonate.
  3. High calcium limestone contains less than 5% magnesium carbonate.
Limestone is quarried or mined then crushed and screened to serve a wide variety of applications including:
  1. pH adjustment (Ag-Lime, water treatment)
  2. Formulated product filler (masonry cements, ready mix concrete, asphalt, and joint compounds)
  3. Raw material in the production of glass, pulp & paper, portland cement and steel.
  4. Flue gas desulfurization
  5. Production of stone blocks
QuicklimeQUICKLIME PRODUCTS:

Limestone is burned (calcined) to create quicklime consisting of calcium and magnesium oxides.

Limestone is converted to quicklime through calcination in energy efficient rotary or vertical kilns. These kilns are normally operated at temperatures exceeding 2000 F.

This product is used for a wide variety of environmental and industrial applications. Major uses of quicklime are as a steel fluxing agent, flue gas desulfurization (FGD) and numerous other environmental applications. Quicklime is also a key component in the production of fiberglass, aluminum, pulp and paper, uranium, gold, copper and in many other critical industries.

Lime kiln dust (wet or dry) consists of partially calcined quicklime and coal fly ash. Applications for this mineral-rich material include environmental treatments, as a raw material for cement production, soil stabilization and as a neutralizing agent in agricultural applications.


HYDRATED LIME PRODUCTS:

Quicklime can be converted into a fine, dry powder called hydrated lime by adding water (hydration) under controlled conditions.

The hydration of calcium oxide occurs readily at atmospheric pressure. Magnesium oxide hydration however, requires a long soak period and/or high pressure levels to completely hydrate. Because of this difference, there are two types of dolomitic hydrated lime. Type N is normally produced at atmospheric pressure. This results in a calcium hydroxide/magnesium oxide product which has high chemical availability. Dolomitic Type S hydrated lime is produced at elevated pressures to completely hydrate the calcium and magnesium compounds.

Hydrated lime is used in many applications including water and waste treatment, soil stabilization, agricultural applications, asphalt modification and flue gas desulfurization. These products are used in many of the same applications as quicklime but hydrated lime products are more chemically dilute than quicklime. They are used in industrial applications where controlled sizing is needed or where slakers are not utilized. Hydrated lime normally does not give off heat when it is combined with water.

Hydrated lime is used as a component in building products such as mortars, plasters, whitewash and stuccos. For building lime products, two different types of hydrated lime products are defined in ASTM standards:

  • Type N or Normal hydrated lime products are only partially hydrated and/or have poor workability. Additional additives and/or long soak periods are required for these products to perform effectively in building applications. At least a 24 hour soak period is required before Type N dolomitic hydrated lime can be used acceptably for masonry or plaster applications. High calcium hydrated lime products normally are classified as Type N hydrates due to their poor water retention. ASTM C270 (Mortar for Unit Masonry) states that if a portland cement/lime blend contains Type N hydrated lime, the blender must show through performance or testing that the Type N product is not detrimental to the soundness of the mortar.

  • Type S or Special hydrated lime products are a combination of calcium and magnesium hydroxides. Type S hydrated lime products are characterized by their chemical purity, high level of hydration and water retention. In building applications, Type S hydrated lime products have high hydration levels and controlled plasticity (water retention). This allows for minimal soak periods prior to application. Though there are some high calcium Type S hydrated lime products, most building lime applications utilize Type S dolomitic hydrated lime.
Air entrainment additives can be added to either category of hydrated lime product. Air entrained products are defined as Type NA or Type SA in ASTM C207. ASTM C207 limits the amount of air content for portland cement/lime (PCL) mortars to 12% for a Type M or S mortar and 14% for Type N and O mortars. If the application involves structural reinforcement, air content cannot exceed 12% in any type of PCL mortar. Air entrainment additives enhance the workability of the mortar blend. As air content increases, bond strength of the mortar decreases.

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