Abstract: Both a system and method are provided for purifying contaminated raw water into potable water by freezing. The system of the invention includes an ice grid having heat exchange surfaces that define cavities for producing ice solids having a surface to volume ratio no greater than 25 to 1, a refrigeration unit for indirectly cooling the heat exchange surfaces to at least the freezing point of the raw water, and an array of spray nozzles that continuously flows raw water over the cavities of the ice grid such that ice solids form from substantially pure water incrementally built up from the heat exchange surfaces of the grid to ultimately fill the grid cavities. The raw water is frozen slowly enough so that unfrozen contaminants expelled from the incrementally freezing ice are continuously washed away from the surface of the growing ice by a continuously raw water flow.

Abstract: This invention relates to apparatus and processes for the removal and recovery of concentrated acid such as HNO.sub.3 and radioactive cations such as cesium (Cs.sup.+) from a radioactive acidic waste stream resulting in the recovery of a decontaminated water product. The invention employs a combination of membrane electrodialysis stacks with each having its own specific cell configuration for performing a specific salt removal or salt concentrating step in the decontamination process.