Calcium Carbonate

Calcium carbonate (CaCO3) is composed of three elements which are of particular importance for all organic and inorganic material on Earth: calcium, carbon, and oxygen. It exists only on Earth and possibly on Mars. It is a simple salt of carbonic acid which results from the reaction of carbon dioxide with burned or slaked lime.

CaCO3 exists in nature as minerals aragonite, calcite and vaterite. Egg shells are 94% calcium carbonate. Limestone is natural source of technical or agricultural grades. Oyster shells are composed largely of calcium carbonate.

CaCO3 is very difficult to dissolve in water. Solubility is just 13 milligrams per liter, and it is the carbonate ion that goes into solution as a hydrogen carbonate ion:

CaCO3 + CO2 + H2O Ca(HCO3)2

In daily life the measuring unit for the amount of dissolved calcium carbonate is water hardness. The United States Geological Survey uses the following classification into hard and soft water:

Constituent of Struvite Stones

Struvite stones are caused by urease-producing bacteria, of which the most common are Proteus, Pseudomonas, Klebsiella, Providencia, E. coli, Staphylococcus epidermis, and Ureaplasma. Urease catalyzes the breakdown of urea and water to ammonium and bicarbonate, thus leading to very alkaline urine. Alkaline urine facilitates the precipitation and crystallization of magnesium ammonium phosphate, calcium carbonate, and calcium phosphate crystals3.



Therapeutic Uses

Calcium carbonate is used therapeutically as a phosphate buffer in hemodialysis patients and as a calcium supplement. Along with calcium citrate, it is the most common form of supplemental calcium. Generally fewer tablets of calcium carbonate are required to achieve given dose of elemental calcium because calcium carbonate generally provides 40 percent elemental calcium, compared with 21 percent for calcium citrate2. Approximately one-fifth to one-third of orally administered calcium is absorbed in the small intestine, depending on presence of vitamin D metabolites, pH in lumen, and on dietary factors, such as calcium binding to fiber or phytates4.

Calcium carbonate is also used as an antacid, a substance that counteracts or neutralizes acidity of the gastrointestinal tract. As antacid it is known under the following names: Neoanticid, Aeromatt, Albaglos, Calcicoll, Calcitrel, Calibrite, Calseeds, Caltrate, and Calwhite. Calcium carbonate is slowly solubilized in stomach and reacts with hydrochloric acid to form calcium chloride, carbon dioxide, and water. About 90% of calcium chloride formed is converted to insoluble calcium salts (mainly calcium carbonate and to lesser extent calcium phosphate) and calcium soaps in small intestine and is not absorbed4.

References

  1. F. Wolfgang Tegethoff, Johannes Rohleder, Evelyn Kroker. Calcium Carbonate: From the Cretaceous Period Into the 21st Century
  2. Dietary Reference Intakes for Calcium and Vitamin D. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, et al., editors.
  3. Spinal Cord Medicine: Principles and Practice. Lin VW, Cardenas DD, Cutter NC, et al., editors.
  4. Calcium Carbonate