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 5 kW m(-2) was maintained in the crystallizer. Sodium carbonate decahydrate with molybdenum content below 1 ppm and pure ice were produced by continuous crystallization at -3.8 degrees C by operating within the metastable zone width of bicarbonate. At -4.0 degrees C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.