Eutectic freeze crystallization from the ternary Na2CO3-NaHCO3-H2O system. A novel scraped wall crystallizer for the recovery of soda from an industrial aqueous stream

Abstract

Eutectic freeze crystallization was tested in a scaled up version of a scraped cooled wall crystallizer on an industrial aqueous sodium carbonate-sodium bicarbonate waste stream containing traces of molybdenum. A heat transfer rate of 5kWm-2 was maintained in the crystallizer. Sodium carbonate decahydrate with molybdenum content below 1ppm and pure ice were produced by continuous crystallization at -3.8°C by operating within the metastable zone width of bicarbonate. At -4.0°C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product. © 2009 The Institution of Chemical Engineers.