Pickling of refractory metals

Process for surface finishing of tantalum parts in the course of mill processing or product fabrication to remove lubricant residue and surface contaminants comprising pickling the metal in an aqueous pickling solution for 5 to 100 minutes at 10 to 50° C., the solution comprising 100 to 400 g/l HF, 10 to 50 g/l H2O2, the bath being entirely free of nitrous oxide precursors;

• treating the bath by addition of an alkali metal fluoride to form an alkali metal tantalum fluoride double salt that crystallizes out of solution in a form usable as a tantalum precursor and recovering the double salt while substantially avoiding salt deposition on the pickled tantalum/niobium surface;
• and
• operating the process substantially continuously with continuous or periodic:
• (a) removal of the double salt, (b) addition of the fluoride, and (c) replenishment of pickling solution components.