Calcium Carbonate calcium
White powder,mainly used as the Ca supplyments.
Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid, but excessive consumption can be hazardous.
| Contents[hide]1 Chemical properties 2 Preparation 3 Occurrence 4 Geology 4.1 Carbonate compensation depth 5 Uses 5.1 Industrial applications 5.2 Health and dietary applications 5.3 Environmental applications 6 Calcination equilibrium 7 Solubility 7.1 With varying CO2 pressure 7.2 With varying pH 7.3 Solubility in a strong or weak acid solution 8 See also 9 References 10 External links |
Industrial applications
The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or limestone aggregate for roadbuilding or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln. However due to erosion mainly caused by acid rain calcium carbonate (in limestone form) is no longer used for building purposes on it's own, and only as a raw/primary substance for building materials.
Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. Calcium carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.[3]
Calcium carbonate is also used in the oil industry in drilling fluids as a formation bridging and filtercake sealing agent and may also be used as a weighting material to increase the density of drilling fluids to control downhole pressures.
Calcium carbonate is also one of the main sources used in growing Seacrete, or Biorock.
Precipitated calcium carbonate, pre-dispersed in slurry form, is also now widely used as filler material for latex gloves with the aim of achieving maximum saving in material and production costs.[4]
Calcium carbonate is widely used as an extender in paints,[5] in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble.
Calcium carbonate is also widely used as a filler in plastics.[5] Some typical examples include around 15 to 20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. PVC cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity). Polypropylene compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high use temperatures.[6] It also routinely used as a filler in thermosetting resins (Sheet and Bulk moulding compounds)[6] and has also been mixed with ABS, and other ingredients, to form some types of compression molded "clay" Poker chips.
Fine ground calcium carbonate is an essential ingredient in the microporous film used in babies' diapers and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching.
Calcium carbonate is also used in a wide range of trade and do it yourself adhesives, sealants, and decorating fillers.[5] Ceramic tile adhesives typically contain 70 to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting stained glass windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature.
Calcium carbonate is known as whiting in ceramics/glazing applications,[5] where it is used as a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze.
Ground Calcium Carbonate (GCC) or Precipitated Calcium Carbonate (PCC) is used as a filler in paper. GCC and PCC are cheaper than wood fiber, so adding it to paper is cost efficient for the paper industry. Printing and writing paper can be made of 10 - 20% calcium cabonate.
In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper. Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. Carbonates are available in forms: ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC). The latter has a very fine and controlled particle size, on the order of 2 micrometres in diameter, useful in coatings for paper.
It is used in swimming pools as a pH corrector for maintaining alkalinity "buffer" to offset the acidic properties of the disinfectant agent.
It is commonly called chalk as it has traditionally been a major component of blackboard chalk. Modern manufactured chalk is now mostly gypsum, hydrated calcium sulfate CaSO4·2H2O.
Ground calcium carbonate is further used as an abrasive (both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has the relatively low hardness level of 3 on the Mohs scale of mineral hardness, and will therefore not scratch glass and most other ceramics, enamel, bronze, iron, and steel, and have a moderate effect on softer metals like aluminium and copper.
