Stalactite CaCO

Stalactites and stalagmites are conical, icicle-like shapes of pure CaCO that form on roofs and floors, respectively, of caverns. These are precipitated from cold groundwater that drips from limestone crevices. 

Thus, water dripping from the ceiling of a cavern can deposit CaCOs a tiny particle at a time, and over long periods can form stalactites and stalagmites. 

Precipitation reactions are important in industry, medicine, and everyday life. For example, the preparation of many essential industrial chanicals such as sodium carbonate (NajCOs) is based on precipitation reactions. The dissolving of tooth enamel, which is mainly made of hydroxyapatite [Ca5(P04)30H], in an acidic medium leads to tooth decay. Barium sulfate (BaS04), an insoluble compound that is opaque to X rays, is used to diagnose ailments of the digestive tract. Stalactites and stalagmites, which consist of calcium carbonate (CaCOs), are produced by a precipitation reaction, and so are many foods, such as fudge. 

Recall from Section 1.3.1 that the mass balance equations (Eqs. 1.1a and 1.1b) contain internal source and sink terms which are due to chemical reactions. Chemical reactions result in the transformation of one chemical substance into another. In environmental media, i.e., sinface waters, the subsurface, and the atmosphere, chemical reactions may occur abiotically or be biologically mediated by organisms. Examples of abiotic chemical reactions include dissolved limestone (CaCOs) precipitating from dripping water to form a solid-phase stalactite or stalagmite in a cave, the attenuation of nuclear fallout over time, the degradation into dust of... 

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