Sulaiman
International Hazard
Posts: 3695
Registered: 8-2-2015
Location: 3rd rock from the sun
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Purification by crystallisation question(s)
I've done a few recrystallizations,
in the case of silver nitrate I had to do many to visually remove 0.1% copper.
What the final purity is, I can only guess.
Is there any way to guesstimate impurity reduction per recrystallization?
eg "impurities are typically reduced by a factor of (insert number here) per recrystallization"
or
tables/graphs for various salts
etc.
I don't know where to look.
...................
Is it just ratios of solubilities (for each substance) at different temperatures?
Seems too easy 
CAUTION : Hobby Chemist, not Professional or even Amateur
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RU_KLO
Hazard to Others
Posts: 209
Registered: 12-10-2022
Location: Argentina
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Found this, maybe you could get information thats applicable to different situations
Purification by crystallization from solutions of various viscosities
https://www.sciencedirect.com/science/article/abs/pii/S00220...
"Generally, crystal growth rate depends on the component system. Furthermore, purification by crystallization depends mainly on crystal growth rate,
that is, the lower the crystal growth rate is, the more pure the crystals are if the viscosity of the solutions is constant. The present work shows
that a linear crystal growth rate does not explain the impurity results obtained from potassium sulfate solutions of various viscosities"
Control of Product Quality in Batch Crystallization of Pharmaceuticals and Fine Chemicals. Part 1: Design of the Crystallization Process and the
Effect of Solvent
https://doi.org/10.1021/op050049v
"The product quality in a crystallization process refers to the crystal size distribution (CSD), crystal morphology, polymorphic outcome and the
degree of crystallinity, and purity. In addition, the product yield is also important. Properties such as the filterability and solid bulk density are
directly related to the CSD. To obtain the desired product quality, attention should be paid to the various operating conditions such as the local and
average levels of supersaturation, the type of the solvent, the operating temperature and pressure, the type and concentration of impurities and
tailor-made additives, degree of mixedness, geometry and the mode of operation of the crystallizer, and seeding and feeding policies. In addition to
these variables, the implementation of external control either in the form of a feedback controller or an optimal control policy can further improve
the product quality"
it seem not trivial and a lot of to take into account
Go SAFE, because stupidity and bad Luck exist.
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