New method for treatment of waste pickling acid

About 55,000 tons of cold rolled steel sheets are produced every month at the Hirohata Works of Fuji Iron & Steel Co. Before cold rolling the hot-rolling coils are subjected to sulphuric acid pickling entailing 4500 to 6000 m3 of waste pickling acid per month. In an attempt to utilise the sulphuric acid contained in the waste pickling acid, a new process of manufacturing iron oxide and ammonium sulphide has been developed, based on the Ishihara Oxidation Method, wherein ferrous sulphide in the waste acid is combined with ammonia and air to produce magnetite with slight absorption of water. This magnetite is precipitated and filtered and its ammonium sulphite is thus recovered. Our process is a modification of the above and is characterised by the following distinct features: the waste acid is neutralised with ammonia contained in the coke gas; the ammonium sulphide produced has equally good size distribution and colour as synthetic ammonium sulphide and iron oxide is also recovered. (Mr. Kiheiji Tamaki, Chemical Section, Chemical Dept., Hirohata Works, Fuji Iron and Steel Co. Ltd., Japan)IRO