Abstract: The invention is directed to a freeze crystallization subassembly having means for continuously removing crystals formed on a heat transfer surface from the surface. A scraper shuttle is moved across the heat transfer surface by a fluid being refrigerated to remove crystals from the surface. The crystals are carried to a mixer where they are mixed with incoming feed until a circulating slurry is produced. Means is provided to remove slurry from the mixer.

Abstract: The invention relates to an apparatus for and method of preparing a slurry for a purification apparatus such as a wash column. A slurry is produced in a crystallizer. The crystals are essentially removed from the concentrated mixture and transported to a more dilute solution. The crystals are caused to dwell in the dilute solution to permit the crystals to ripen and to grow in size significantly.The apparatus that performs the foregoing functions is a gradient column where the change from a concentrated slurry to a dilute slurry takes place. The output of the gradient column is coupled to a holding tank where the residence time of crystals in the dilute solution is prolonged to permit the crystals to ripen.