Calcium carbonate

Calcium Carbonate (CaCO₃)

Calcium carbonate is a naturally occurring inorganic compound with the chemical formula CaCO₃. It is one of the most common minerals on Earth, widely found in limestone, marble, shells, pearls, eggshells, etc.  

1. Basic Properties 

- Chemical formula: CaCO₃  

- Molar mass: 100.09 g/mol  

- Appearance: White powder or odorless crystals (different crystal forms)  

- Solubility:  

- Almost insoluble in water (solubility ~0.0014 g/100 mL, 25°C)  

- Soluble in acids, releasing CO₂: 

- Thermal stability: Decomposes at 825°C into calcium oxide (CaO) and carbon dioxide (CO₂):  

2. Main Crystal Forms (Polymorphs)

Calcium carbonate has three common crystal structures, which affect its physical properties and applications:  

- Calcite

   - Most stable, hexagonal crystal system, used in construction materials and fillers.  

- Aragonite

   - Orthorhombic crystal system, biologically sourced (e.g., shells, corals), used in high-end fillers and biomaterials.  

- Vaterite

   - Least stable, metastable, used in drug sustained-release and nanomaterials.  

3. Main Sources 

- Natural minerals:  

  - Limestone (main component CaCO₃)  

  - Marble (metamorphosed limestone, high purity)  

  - Chalk (formed by microbial deposition)  

- Biological sources:  

  - Shells, eggshells, corals (mainly composed of aragonite-type CaCO₃).  

- Industrial synthesis:  

  - Precipitation method: Bubbling CO₂ into calcium chloride (CaCl₂) solution or adding sodium carbonate (Na₂CO₃):  

4. Main Applications

(1) Industry and Construction Materials

- Cement & Lime: Calcining CaCO₃ to produce quicklime (CaO), used in construction and steel industries.  

- Fillers & Coatings:  

  - Papermaking (improves whiteness and smoothness)  

  - Plastics, rubber (enhances mechanical properties)  

  - Paints (thickening, wear resistance)  

(2) Food and Pharmaceuticals

- Food additive (E170):  

  - Anti-caking agent (e.g., in table salt, milk powder)  

 - Calcium supplement (must meet food-grade standards)  

- Pharmaceutical excipient:  

  - Antacid (neutralizes stomach acid)  

  - Tablet filler  

(3) Agriculture and Environment

- Soil conditioner: Neutralizes acidic soil (raises pH).  

- Water treatment: Removes heavy metals (e.g., Pb²⁺) and acidic pollutants from water.  

(4) Other Applications

- Toothpaste abrasive (mild grinding, cleans teeth).  

- Cosmetics (filler in foundation, powder).  

Laboratory: Preparation of CO₂, calcium standard solutions.  

5. Safety and Precautions 

- Toxicity: Low toxicity, but long-term inhalation of dust may cause pneumoconiosis (industrial protection must meet standards).  

- Food and pharmaceutical grade: Requires high purity (free from heavy metals, arsenic, and other impurities).  

- Storage: Dry environment, avoid contact with acids.