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Q. What is lime? What are the differences between quicklime and hydrated lime, high calcium lime and dolomitic lime?

A: Lime is a generic term, but by strict definition it embraces only the manufactured forms of lime — quicklime and hydrated lime. It does not include limestone, which is the feedstock for lime manufacturing.

Quicklime, the product of calcination of limestone, consists of the oxides of calcium and magnesium, and in Canada it is available in three forms:

  • High calcium quicklime--derived from limestone containing 0 to 5 percent magnesium carbonate.
  • Magnesian quicklime--derived from limestone containing 5 to 35 percent magnesium carbonate.
  • Dolomitic quicklime--derived from limestone containing 35 to 46 percent magnesium carbonate.

Hydrated lime is a dry powder manufactured by treating quicklime with sufficient water to satisfy its chemical affinity for water, thereby converting the oxides to hydroxides. Depending upon the type of quicklime used and the hydrating conditions employed, the amount of water in chemical combination varies, as follows:

  • High calcium hydrated lime--high calcium quicklime produces a hydrated lime containing generally 72 to 74 percent calcium oxide and 23 to 24 percent chemically combined water.
  • Dolomitic hydrated lime (normal)--under atmospheric hydrating conditions only the calcium oxide fraction of dolomitic quicklime hydrates, producing a hydrated lime of the following chemical composition: 46 to 48 percent calcium oxide, 33 to 34 percent magnesium oxide, and 15 to 17 percent chemically combined water.
  • Dolomitic hydrated lime (pressure)--this lime is produced from dolomitic quicklime under pressure, which results in hydrating all of the magnesium oxide as well as all of the calcium oxide, producing the following chemical composition: 40 to 42 percent calcium oxide, 29 to 30 percent magnesium oxide, and 25 to 27 percent chemically combined water.


Q. What about physical specifications for lime?

A: Hydrated lime is available only as a fine powder or a slurry. Normal grades of hydrated lime suitable for most chemical purposes will have 85 percent or more passing a 200-mesh sieve, while for special applications hydrated lime may be obtained as fine as 99.5 percent passing a 325-mesh sieve.

Quicklime, however, is commercially available in a number of sizes (the following definitions are derived from ASTM Standard C51):

  • Large lump lime--a maximum of eight inches in diameter.
  • Crushed or pebble lime--ranging from about ¼ to 2 ½ inches.
  • Ground lime-- ¼ inches and smaller.
  • Pulverized lime--a typical size is substantially all passing a No. 20 sieve.
  • Pelletized lime--one inch sized pellets or briquettes, molded from fines.


Q: What are the differences between Type N, NA, S, & SA hydrated lime used for mortar and other building applications?

A: Hydrated limes used in building applications are divided into four types, as described in ASTM Standard Specification C207 (Hydrated Lime for Masonry Purposes):

  • Type N – normal hydrated lime
  • Type NA – normal air-entraining hydrated lime
  • Type S – special hydrated lime
  • Type SA – special air-entraining hydrated lime

Types S and SA are differentiated from Types N and NA principally by their ability to develop high early plasticity, higher water retentivity, and by their limitation on unhydrated oxide content. The maximum air content of cement-lime mortar made with Types NA and SA is 14%; with Types N or S lime, 7%.


Q: Is aglime the same as lime?

A: The term agricultural lime, or "aglime," usually refers to limestone. Limestone (calcium carbonate) is not the same as hydrated lime (calcium hydroxide).


Q: Do you have a listing of the specifications for lime in various industrial uses?

A: There is an ASTM standard C911, for lime used in chemical (and industrial) uses. Uses addressed include water softening, other water treatment, hypochlorite bleach, silica brick, calcium silicate products, industrial waste treatment, sulfite pulp, and carbide. The standard can be purchased directly from ASTM at www.astm.org.


Q: What procedures should I use to test lime?

A: ASTM has Standard Methods for testing chemical (C25) and physical (C110) properties. These standards can be purchased directly from ASTM at www.astm.org.

 

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