Fractional crystallization (chemistry)
The Fractional crystallization is a separation method of chemistry , the separation of crystallizable substances differences in their solubility uses.
The precipitation of two or more substances present in a solvent from the solution takes place in a different order, because readily soluble substances still remain in solution while poorly soluble substances crystallize out or are separated out earlier. The crystallization or precipitation reaction can be brought about by changes in concentration, changes in temperature or other triggers such as the addition of seed crystals (in almost saturated or supersaturated solutions).
This fact is used in the chemical-technical process of fractional crystallization. The mixture of substances to be separated is mixed with a solvent and heated. During slow cooling, the individual substances crystallize out one after the other so that they can be obtained in pure form from the solution in a suitable device. The process can also be used several times in succession in order to increase the purity of the substances obtained.
Marie Curie used fractional crystallization to separate the chlorides (later the bromides ) from radium and barium , which were originally present in the extracts of the pitchblende in a ratio of 3: 100,000 in order to obtain a few mg of pure radium chloride .
The process is in chemical engineering, not only for the production of chemically pure substances or preparation used by waste, but also as a chemical analysis method used. For example, in the representation of rare earths or the separation of individual lanthanoids from the mixed crystals of these elements that always occur in nature .
See also
- Single crystal
- Crystal structure
- Crystallite
- Recrystallization
- Fractionation
- Fractional crystallization (petrology)
Individual evidence
- ↑ The discovery of radium. BoD - Books on Demand, 2012, ISBN 3864449111 , p. 12 ( limited preview in the Google book search).
- ↑ K. Rossmanith: Pure preparation of neodymium-magnesium double nitrate by fractional crystallization . In: Monthly books for chemistry / Chemical Monthly . tape 25 , no. 6-7 . Springer, Vienna 1994, p. 691-694 , doi : 10.1007 / BF01277628 .
- ↑ The Separation of the Lanthanoids. In: Prof. Blume's media offer. Retrieved February 7, 2010 .