·
Linear Formula CaCO3
·
Molecular Weight 100.09
·
Beilstein Registry
Number 8008338
Calcium carbonate is a chemical
compound with
the formula CaCO3. It is a
common substance found in rocks as
the minerals calciteand aragonite (most
notably as limestone, which contains
both of those minerals) and is the main component of pearls and the shells of
marine organisms, snails, and eggs.
Detailed description
Calcium carbonate is the
active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.
Uses
Industrial applications
The main use of calcium carbonate is in the
construction industry, either as a building material or limestone aggregate for
road building or as an ingredient of cement or as the starting material for the
preparation of builder's lime by burning in a kiln. However, because of
weathering mainly caused by acid rain,[17] calcium
carbonate (in limestone form) is no longer used for building purposes on its
own, but 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. The carbonate is
calcined in situ to give calcium oxide, which forms a slag
with various impurities present, and separates from the purified iron.[18]
In the oil industry, calcium carbonate
is added to drilling fluids as a formation-bridging and filtercake-sealing agent; it
is also a weighting material which increases the density of drilling fluids to
control the downhole pressure. Calcium carbonate is added to swimming pools, as
a pH corrector for maintaining alkalinity and offsetting
the acidic properties of the disinfectant agent.[citation needed]
It is also used as a raw material in the refining of
sugar from sugar beet; It is calcined in a kiln with anthracite to produce calcium
oxide and carbon dioxide. This burnt lime is then slaked in sweet water to
produce a calcium hydroxide suspension for the precipitation of impurities in
raw juice during carbonatation.[19]
Calcium carbonate has traditionally been a major
component of blackboard chalk. However, modern manufactured chalk is
mostly gypsum, hydrated calcium sulfate CaSO4·2H2O.
Calcium carbonate is a main source for growing Seacrete, or Biorock. Precipitated
calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler
material for latex gloves with the aim of achieving maximum saving in material
and production costs.[20]
Fine ground calcium carbonate (GCC) is an essential
ingredient in the microporous film used in diapers and some
building films as the pores are nucleated around the calcium carbonate particles
during the manufacture of the film by biaxial stretching. GCC or PCC is used as
a filler in paper because they are cheaper than wood fiber. In terms of market
volume, GCC are the most important types of fillers currently used.[21] Printing and
writing paper can contain 10–20% calcium carbonate. 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. PCC used for paper filling and paper coatings is
precipitated and prepared in a variety of shapes and sizes having
characteristic narrow particle size distributions and equivalent spherical
diameters of 0.4 to 3 micrometres.[citation needed]
Calcium carbonate is widely used as an extender in
paints,[22] in particular
matte emulsion paint where typically 30% by weight of the paint is either chalk
or marble. It is also a popular filler in plastics.[22] 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).[citation needed] Polypropylene compounds are
often filled with calcium carbonate to increase rigidity, a requirement that
becomes important at high use temperatures.[23] Here the
percentage is often 20–40%. It also routinely used as a filler in thermosetting resins (sheet and bulk molding compounds)[23] and has also
been mixed with ABS, and other ingredients, to form some types of compression
molded "clay" poker chips.[citation needed] Precipitated calcium carbonate, made by
dropping calcium oxide into water, is used by itself or with additives as a white
paint, known as whitewashing.[citation needed]
Calcium carbonate is added to a wide range of trade
and do it yourself adhesives, sealants, and decorating fillers.[22] 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.[citation needed]
In ceramics/glazing
applications, calcium carbonate is known as whiting,[22] and is 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 is 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. A paste made from calcium carbonate and deionized watercan be used to
clean tarnish on silver.[24]
Health and dietary applications
Calcium carbonate is widely used medicinally as an
inexpensive dietary calcium supplement for gastric antacid.[25] It may be used
as a phosphate binder for the treatment of hyperphosphatemia (primarily in
patients with chronic renal failure). It is also used in the pharmaceutical industry as an
inert filler for tablets and
other pharmaceuticals.[26]
Calcium carbonate is used in the production of
calcium oxide as well as toothpaste and has seen a resurgence as a food
preservative and color retainer, when used in or with products such as organic
apples.[27]
Excess calcium from supplements, fortified food and
high-calcium diets, can cause milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram
Sippy introduced the "Sippy regimen" of hourly ingestion of milk and
cream, and the gradual addition of eggs and cooked cereal, for 10 days,
combined with alkaline powders, which provided symptomatic relief for peptic
ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failure, alkalosis, and hypercalcaemia, mostly in men with
peptic ulcer disease. These adverse effects were reversed when the regimen
stopped, but it was fatal in some patients with protracted vomiting.
Milk-alkali syndrome declined in men after effective treatments for peptic ulcer disease arose.
During the past 15 years, it has been reported in women taking calcium
supplements above the recommended range of 1.2 to 1.5 g daily, for
prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been
added to over-the-counter products, which contributes to inadvertent excessive
intake. Excessive calcium intake can lead to hypercalcemia, complications of
which include vomiting, abdominal pain and altered mental status.[28]
As a food additive it is
designated E170;[29] INS number
170. Used as an acidity regulator, anticaking agent, stabiliser or colour it is
approved for usage in the EU,[30] USA[31] and Australia and New Zealand.[32] It is used in
some soy milk and almond milk products as a
source of dietary calcium; one study suggests that calcium carbonate might be
as bioavailable as the calcium in cow's milk.[33] Calcium
carbonate is also used as a firming agent in many canned
or bottled vegetable products.
Agricultural use
Agricultural lime, powdered chalk or limestone, is used as a cheap method for
neutralising acidic soil, making it suitable for planting.
PRICE
$675.71/KG OR $307.14/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
No comments:
Post a Comment