SELECTIVE SEPARATION OF IRON AND CHROMIUM FROM STAINLESS STEEL SPENT PICKLING

Stainless steel spent pickling baths are very complex solutions of metals and acids (HNO3 and HF) and are a very, important environmental concern. Several processes have been developed for acid recovery (free and bounded acid) with techniques like acid retardation, solvent extraction, evaporation and dialysis diffusion. In these processes, metallic content is precipitated and treated for its disposal. We have developed a process that permits the separation of metals by means of a selective precipitation, induced by adding free fluoride. Iron (Fe) and chromium (Cr) precipitate as pentafluorides and nitrogennickel (Ni) remains in solution. After this stage, complex fluorides can be hydrolized with alkali to give iron and chromium hydroxides, releasing fluoride in solution.