Hard-burned dolomite

Hard-burned dolomite is generally produced in mixed-feed shaft kilns, operating under reducing conditions. Hard-burned dolomite is generally produced in mixed-feed shaft kilns, operating under reducing conditions. 

Hardness. Most commercial quicklime products have a hardness of 2 to 3 Mohs. The value for dead-burned dolomite is in the range 3 to 5 Mohs [13.1]. 

As described in section 20.3.1, other causes of grit are calcium carbonate and hard-burned lime. The production of grit is minimised by pulverising the lime and many processes reduce the particle size to below 10 mm and, in some cases, to below 5 mm. Dolomitic lime is generally ground more finely (see section 20.7). 

The rotary kiln has become extremely important in lime processing, and is used to burn a large portion of dolomitic quicklime production. More than half of all industrial quicklime is made in rotary kilns. The rotary is particularly useful for making the hard burned grade of quicklime that must contain a minimum amount of unburned limestone. 

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). 

Four qualities of calcined dolomite are produced — half-, light-, hard-, and dead-burned. 

A relatively "hard-to-burn" feed from the western U.S., with a very impure dolomitic limestone, has 6.7% >125 pm and an acetic-acid insoluble residue of 9.5% >45 pm, the latter comprised of quartz, feldspar, medium to finely crystalline igneous and metamorphic rock fragments, and an abundance of ferro-magnesian minerals (mainly amphiboles and pyroxenes). = 1.6% and = 4.5%. Belite nests (many with tightly packed crystals), solitary belite, and periclase are abundant in this fine- to medium-crystalline clinker. Nevertheless, a high-compressive strength mortar (44.8 to 48.3 MPa) is made, mainly because of the small alite size and the well-scattered solitary belite. 

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