Pickling acid regeneration by electroplating and electrodialysis - where ammonium ions are added to spent hydrochloric acid pickle to improved regeneration

摘要

An appts. is used which includes an anode chamber sepd. by a cationic membrane from a middle chamber. The middle chamber is sepd. from a cathode chamber by an anionic membrane; and in the cathode chamber is a cathode, on which iron in a spent HCl pickling soln. is deposited by electroplating, while the spent soln. is simultaneously enriched with HCl in the middle chamber. To improve the selectivity of the anionic membrane w.r.t protons, an ammonium cpd. is added to the middle chamber to provide NH4 ions in the soln. The NH4 ions are pref. obtd. by bubbling NH3 gas into the soln. or by adding an ammonium salt. An earlier patent, FR2273082, describes a similar process for the regeneration of spent pickling acid, but the anionic membrane has inadequate proton selectivity, esp. in conc. HCl used for pickling prior to hot dip galvanishing. The present invention solves this problem.