Hydrochloric acid pickling soln. regeneration with cold sulphuric acid - giving ferrous sulphate hepta:hydrate as useful by=product

摘要

In the regeneration of pickling solns. contg. HCl by adding conc. H2SO4, the soln. is kept at a temp. below 45 deg. C. Reaction between H2SO4 and Fe chloride is carried out in vacuo. Cold centrifuge filtrate contg. H2SO4 is pref. used as cooling medium. USE/ADVANTAGE - The process is esp. used for regenerating solns. used for pickling steel strip. All the FeCl2 present is converted to FeSO4.7H2O, which is readily soluble and can be used for various purposes, e.g. H2SO4 recovery, dyestuff prodn. or water treatment. In contrast, regeneration with conc. H2SO4 at over 50 deg.C gives FeSO4.H2O, which is insoluble in water and cannot be recovered economically, whilst roasting gives Fe2O3 and entails a high energy consumption.