Patent ID: 6210558
Filing Date: 2001-04-03
Classification: C23G

Abstract:
Pickling process for stainless steel, wherein a pickling solution is used which contains as essential components HF and Fe.sup.3+ ions, and the oxidation to Fe.sup.2+ formed during the pickling process, in order to maintain the concentration of Fe.sup.3+ at the predetermined value, is carried out electrolytically by subjecting the pickling solution as it comes out from the pickling bath to an anodic oxidation process in an electrolytic cell provided with anode made of a material inalterable to the anodic oxidation and characterized in that the electrolytic cell is provided with a diaphragm separating the cathodic area from the anodic one, said diaphragm being made of porous material or consisting of an ion exchange membrane, the anode is made of graphite or other carbonaceous materials, the cathode, suitable for the cathodic reduction of cations H.sup.+ and consequent development of gaseous hydrogen, is made of ferrous or carbonaceous materials or of a metal chosen amongst zirconium, titanium, tantalum, tungsten, vanadium, and in that the cell voltage is comprised between 1 and 8 V and the anodic current density is comprised between 0.4 and 15 A/dm.sub.2 and further characterized in that the thus obtained re-oxidized solution is recycled directly to the pickling bath.