Pickling baths contg. iron - purified by heating, neutralising to control pH and oxidising ferrous to ferric ions

摘要

pickling baths from surface-treatment works are treated to selectively ppte. the iron. Soln. between 60 degrees C and soln. b.pt. pH is set to 2-5 (3-4). A neutraliser si added slowly to maintain soln. pH within given limits. An oxidising agent is added at the same time, to effect a slow oxidn. of Fe2+ in soln. to Fe3+, which can be pptd., e.g. as Fe2O3. After selective Fe pptn. at pH 5, pH is slowly increased to 9-10, between 60 degrees C and soln. b.pt. Zn and other metal ions are pptd. as a suspension having favourable physical properties. Pptn. conditions for Fe and other metal salts are improved. Pptes. have properties allowing easy separation. In an example, Fe and Zn contents were reduced from 119 g/l and 68 g/l to 1 mg/l and 3 mg/l respectively.