Eutectic freeze crystallization is a novel technique for processing waste and process streams of aqueous electrolyte solutions, separating them into pure water and pure solid salt. A dedicated apparatus, a 100-L cooled-disk column crystallizer, has been developed and tested, combining crystallization and solid/solid separation of ice and salt. Experiments have been performed with a ternary system of aqueous KNO3-HNO3. Heat-transfer rates were achieved in the range of 1300-4600 W.m(-2).K-1, which are related to the square root of the scraping rate. The ice product slurry contained 0.15 wt % salt. The ice impurity content after three washing cycles was as low as 15 ppm K+. Well-faceted KNO3 crystals are produced with high purity.