Abstract: Waste water containing large amounts of fluorides and ammonia and trace amounts of uranium, as is produced during the hydrolysis and ammonium hydroxide treatment of uranium hexafluoride (UF.sub.6) to produce ammonium diuranate (ADU) therefrom, is rendered suitable for cyclic reuse by initially treating the waste water with sufficient lime to precipitate substantially all of the fluorides present in the waste water to a relatively insoluble CaF.sub.2 precipitate, the treated solution is subjected to distillation to drive off ammonia for reuse in the ADU precipitation, the CaF.sub.2 precipitate is separated from the aqueous distilland leaving water with dissolved calcium, the distilland is treated by a cationic ion-exchange material to remove substantially all of the calcium and other cationic metal impurities and the resulting water containing small amounts of uranium, fluoride and ammonia is recycled to react with UF.sub.