CALCIUM CARBONATE
~ also known as Limestone; 471-34-1; Chalk; Calcite; Carbonic acid calcium salt (1:1); etc. is the carbonic salt of calcium. It is a common substance which can be found in rocks and is the main constituent of pearls and the shells of snails, marine organisms, and eggs. The global market for Calcium Carbonate is estimated to reach 98.7 million tons by 2020, due to the robust demand from paper and plastics end-use sectors.
Chemical structure: CaCO3 or CCaO3. The thermodynamically stable form of CaCO3 under standard conditions is hexagonal β-CaCO3, (the mineral calcite). There are other less stable forms, they include; orthorhombic λ-CaCO3 (mineral aragonite) and μ-CaCO3 (mineral vaterite).
Properties: calcium carbonate is a white, colorless crystal or odorless powder. It is non-corrosive but virtually insoluble in water and in alcohol. It dissolves with effervescence in diluted hydrochloric acid, in diluted acetic acid, and in diluted nitric acid, and the resultant solutions, after boiling, provide positive tests for calcium. When heated to decomposition, it gives off acrid smoke and irritating vapors.
Production:Â
- The large majority of calcium carbonate used in the industry is extracted by quarrying or mining. Pure calcium carbonate (used for food or pharmaceutical purposes), may be produced from a pure quarried source.
- On the other hand, calcium carbonate can be prepared from calcium oxide. Water is introduced to give calcium hydroxide. Then carbon dioxide is added to this solution to precipitate the preferred calcium carbonate. In the industry, this is called precipitated calcium carbonate (PCC):
CaO + H2O → Ca(OH)2
 Ca ( OH ) 2 + CO 2 ⟶ CaCO 3 ↓ + H 2 O {\displaystyle {\ce {Ca(OH)2 + CO2 –> CaCO3(v) + H2O}}}
Chemical reactions and Uses: Calcium carbonate shares the usual properties of other carbonates.
- It reacts with acids to release carbon dioxide:
CaCO3(s) + 2H+(aq) → Ca2+(aq) + CO2(g) + H2O (l)
- It releases carbon dioxide when heated to form calcium oxide, usually called quicklime, with reaction enthalpy of 178 kJ/mole:
CaCO3 (s) → CaO (s) + CO2 (g)
Calcium carbonate reacts with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.
CaCO3 + CO2 + H2O → Ca(HCO3)2
This reaction is vital in the erosion of carbonate rock and leads to hard water in many regions.
The major use of calcium carbonate is in the construction industry. It is used either as a building material or limestone mass for road building or as a constituent of cement or as the preliminary material for the preparation of builder’s lime. Calcium carbonate is also utilized in the refining of iron from iron ore in a blast furnace. In the oil industry, calcium carbonate is introduced to drilling fluids. It is also utilized as a raw material for refining sugar from sugar beet. Calcium carbonate has by tradition been a major constituent of blackboard chalk. Fine ground calcium carbonate (GCC) is an important constituent in the microporous film used in diapers. Calcium carbonate is extensively used as an extender in paints. Calcium carbonate is used in a wide array of sealants, adhesives, and decorating fillers. In ceramics/glazing use, calcium carbonate is known as whiting.
In medicine, Calcium carbonate is broadly used as a low-cost dietary calcium supplement for gastric antacid. It is utilized in the production of calcium oxide and toothpaste.
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