Calcite particle size distribution

Accurate comparison of results requires knowledge of reaction site density per unit surface area. Calcite materials used for kinetic study have included natural marbles, limestones, hydro-thermal crystals of Iceland spar, tests of calcareous organisms and laboratory and commercial precipitates. Surface areas, estimated by BET methods and graphical methods (based on particle size distribution) range from about 0.005 to 2 m g . There are apparent discrepancies between graphical and BET surface areas and the question is raised as to which type of surface area estimate is most representative of the reacting surface area. 

The rate of calcite dissolution is a function of the solution composition and particle size distribution. The rate should be independent of surface roughness, internal surface area, and other variables. 

A microcrystalline limestone, as opposed to a limestone made of coarse fossil shells and other calcite particles, was shown to grind differently, producing a raw meal with a relatively uniform and finer particle size distribution, leading to an improved burnability (Sas, 1997). 

Premium grades of calcium carbonate command a high price. They include ultrawhite grades, which can be subdivided into subgrades with specified particle size distributions, very fine calcites and surface-coated grades. 

All raw materials purchased by glass producers have to pass very stringent requirements for composition and particle size distribution. Silica is from sand and alumina is from the clay. Boric oxide is from colemanite and boric acid. Limestone or calcite is for calcium oxide. The summary is given in Table 9.1. 

There are also a large number of products produced from heavily compacted limestone, which are known as ground limestones. Their average particle-size distributions will be similar to ground-marble products, while colours can range from fairly pure white to grey. All of these products, because of the rhombohedral cleavage pattern of calcite crystals, consist of (mostly) uniform calcite crystals with a fairly symmetrical aspect ratio of 3 1. 

Naturally occurring forms of calcium carbonate include limestone, chalk, marble, and calcite. After mining, the calcium carbonate is ground, screened and air elassified. Some grades are water washed, water ground and redried. Wet ground grades have smaller particles with a narrower particle size distribution. TTiey are also more expensive. Typieal properties are shown in... 

Marble deposits can be processed in the same way as chalk but, because marble contains different sized calcite crystals, or grains, a wider range of particle sized products, with wider size distributions are obtained, especially as there may be a need to fragment large crystals. Actual particle sizes will depend on the extent of processing, but typical products will have a mean value of 3-5 0,m, with 20-30 wt% finer than 2 pm and a specific surface area around 1 m g ... 

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