Process for regenerating a nitric acid-hydrofluoric acid pickling solution

摘要

In pickling metal, such as iron, steel, special alloys, or the like, aqueous blends containing hydrofluoric acid and nitric acid are used as pickling solutions; resulting spent pickling solutions are evaporated under controlled conditions, such that the concentrate is supersaturated and contains a predetermined amount of iron; the concentrate is then partially cooled and transferred to a crystallization zone where, under controlled conditions, a crystalline precepitate is formed by cooling the concentrate in two phases; the resulting precipitate is then separated from its mother liquor, and the latter is recycled for use in pickling metals of the aforedescribed type.