Limestone Purity test


Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).



Limestone is composed principally of calcium carbonate, which when heated at elevated temperatures decomposes to calcium oxide and carbon dioxide.
    CaCO3     +         Heat     =   CaO + CO2

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The CaCO3 may account for a composition as high as 98.5% or more in limestone, and when broken down, the value of CaO is 55.19%. Limestone, an impure form of calcium carbonate contains other constituents as impurities in addition to the carbon dioxide present.  These are the calcium and magnesium silicates as well as silicates of iron, alumina, manganese, titanium, sodium and potassium. When the combined value of silicates present is high, the CaO value is correspondingly reduced.
On the other hand, limestone may become dolomitic, that is, in addition to CaCO3present; there exists also a large concentration of MgCO3 in the form of CaCO3. MgCO3 in which case the MgO is very large and may reach up to 21% plus. However, the CaO content is much reduced compared to the concentration in a principally CaCO3 limestone.
The analysis of limestone, irrespective of its nature entails as a primary step, a decomposition reaction with dilute hydrochloric acid to form mainly a solution of calcium chloride from which the various other chemical constituents are derived in a stepwise manner by the application of suitable analytical procedures. The parameters to be determined are: CaO, MgO, (Fe2O3, TiO2, Al2O3) or a combination of these as R2O3, Acid insoluble component or silica, and Loss on ignition or carbon dioxide (CO2).
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