precipitation

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In chemistry, precipitation or precipitation (from the Latin praecipitatio "falling down") describes the elimination of a dissolved substance from a solution . This is done by exceeding its solubility due to changes in its environmental conditions, e.g. B. by adding suitable substances ( precipitants ), temperature and pressure changes , evaporation of the solvent or changing the polarity of the solvent. The precipitation occurs as a precipitate in the form of amorphous flakes or crystalline material. Basically there is a phase transition of the previously dissolved substance.

Limescale deposits on a leaky shut-off valve

An added precipitating agent can become part of the precipitate or convert the dissolved substance into a more sparingly soluble one, or only change the solubility properties of the solvent. The precipitates of the precipitated solids are initially mostly microcrystalline or amorphous . Over time, recrystallization can lead to the formation of a more stable crystal modification. Often these particles enlarge as they age due to additional agglomeration . This allows them to be filtered better or to form a sediment. As the precipitates age, their solubility often decreases further.

The formation of the precipitate or precipitate by precipitation can be triggered in several ways, by precipitation reactions , changing the pH value or exceeding the solubility product .

Precipitation of uranyl carbonate

In biochemistry , precipitation is specifically the precipitation of proteins or nucleic acids . The effect of certain salts on the solubility of corresponding organic compounds is characterized using the Hofmeister series . Special precipitation methods in biochemistry include ammonium sulfate precipitation , PEG precipitation , TCA precipitation (denaturing), ethanol precipitation (denaturing) and heat precipitation (denaturing).

In wastewater treatment , in addition to precipitation with precipitants, flocculation with the use of flocculants or flocculants is often used to remove colloidally dissolved ingredients .

Coprecipitation

Coprecipitation is a special form of precipitation in which the starting materials are first brought into solution in order to ensure homogeneous distribution. Then, by mixing the two solutions or adding another solution, a precipitation reaction occurs. a. Form hydroxides or carbonates. The now homogeneous solid mixture can then be filtered and further processed. This further processing can, for example, be firing in a furnace (e.g. for nickel aluminate synthesis).

See also

Web links

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Individual evidence

  1. ↑ S. Ebel and HJ Roth (editors): Lexikon der Pharmazie , Georg Thieme Verlag, 1987, p. 464, ISBN 3-13-672201-9 .
  2. ^ Alfred Pingoud : Working methods of biochemistry. Walter de Gruyter, 1997, ISBN 978-3-110-16513-5 , pp. 53-56.
  3. ↑ Philipp Kurz, Norbert Stock: Synthetic Inorganic Chemistry: Basic Course . Walter de Gruyter, Berlin 2013, ISBN 978-3110258745 , p. 41.