Calcined dolomite or simply dolomite or dolomite (i.e., CaO + MgO) is a product produced by calcination at relatively low temperatures and is highly porous and reactive. Like other carbonates, upon heating above 900°C dolomite decomposes completely into a mixture of calcium and magnesium oxides, and carbon
dioxide:
CaMg(CO3)2(s) —> CaO(s) + MgO(s) + 2CO2(g)
Dead burned dolomite exhibits high refractoriness and
can withstand temperatures up to 2300°C. It is widely used as a refractory material wherever
steel is refined using basic slag. It is used for original hearth installations in open hearth
furnaces as well as for hearth maintenance. These hearths are installed using tar-dolomite
ramming mixes and rammed dolomite. Dolomite refractories are also used in electrical furnaces and in the cement industry during clinker manufacture.
Dead burned refractory dolomite is produced in vertical shaft or
rotary kilns. Generally high-purity dolomite, with total impurities of less than 3 wt.%, is
selected. As it is difficult to densify high-purity dolomite in a rotary kiln, it is customary to
use some mineralizers to facilitate sintering. Iron sesquioxide is a common additive. The
manufacturing process varies with the grade of dead burned dolomite needed. Most plants
use rotary kilns lined in the hot zone with basic bricks and fired with powdered coal. The
temperature reached in the hot zone is ca. 1760°C or above when iron oxide is added. After
dead burning, dead burned dolomite is cooled in either rotary or reciprocating recuperative
coolers. The air used for cooling gets heated and is again used as secondary air for combustion in the kilns.
