Soft-burned quicklime

Hardness. Most limestone is soft enough to be readily scratched with a knife. Pure calcite is standardized on Mohs scale at 3 aragonite is harder, 3.5—4. Dolomitic limestone is generally harder than high calcium. Dead-burned or sintered limes are 3—4 on this scale, whereas most commercial soft-burned quicklimes are 2—3 (see Hardness). 

See also Solid oxide fuel cell (SOFC) Soft annealed copper alloys, 7 723t SOFTANOL, 2 43 Soft-burned quicklime, 15 29 Soft coals, 6 703 Soft copolymers, 26 538, 540 Softeners, in tire compounding, 21 809—810 Softening... 

Soft-burned quicklime see light-burned quicklime. 

Soft-burned lime is a quicklime that is calcined at a relatively low temperature. It is characterized by high porosity and chemical reactivity. 

Calcium Oxide. Also called lime or quicklime (4,5), calcium oxide [1305-78-8] (Class 1, nonregenerative), is relatively iaexpensive. It is prepared by roasting calcium carbonate (limestone) and is available ia a soft and a hard form according to the way ia which it was burned. For desiccant service, soft-burned lime should always be used. Calcium oxide is most commonly used to dehydrate Hquids and is most efficient when it can be heated to speed the reaction rate. The reaction product is calcium hydroxide, which cmmbles as it picks up moisture. 

Hard and soft acid and base (HSAB) principle, 16 780 Hard blacks, 21 775 Hard-burned quicklime, 15 28 Hard coals, 6 703 classification, 6 712 Hard copper alloys, 7 723t relief annealed, 7 723t Hard copy systems, 9 513-514 Hard core repulsion, 23 93 Hard-elastic olefin fibers, 11 242 Hardenability, of steel, 23 283—284 Hardened MF resins, analysis of,... 

Table 15.4 Typical properties of soft medium and hard-burned quicklimes.

Oxygen is blown into the molten metal at supersonic speeds through a water-cooled lance for about 15 min. to oxidise some of the impurities. Two to three minutes after the start of the oxygen blow, quicklime (30 to 50 kg/t of hot metal) soft-burned dolomite (10 to 25 kg/t) [27.21] and, optionally, fluorspar (up to... 

There are at least two other critical variables that should be considered when purchasing lime for a chemical plant. Quicklime is usually classed as soft burned, medium burned, and dead or hard burned. The higher the temperature limestone is converted to quicklime, the less reactive it becomes. It can become almost impossible to slake (hydrate) quicklime to calcium hydroxide, if it is cooked at too high temperatures. Cooking limestone is an art and operators become very skill at their trade. 

As limestone is cooked to higher temperatures, the CaO crystal lattice shrinks and the quicklime becomes more and more dense. Soft burned lime is more reactive and can be slaked more easily, but slaking is yet another art form. Other than the source and history of a quicklime, the temperature and concentration of a lime slurry become important variables. In chemical processes it is usually desired that a slaked lime react quickly and completely with other raw materials in the process, such as phosphoric acid. Slaked lime is very sparingly soluble in water and is usually introduced into a process as a slurry. Small particles of lime usually react more rapidly, but not always. 

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