Recovery of ferrous sulfate from basic oxygen furnace sludge using waste sulfuric acid

Basic oxygen furnace (BOF) sludge and waste sulfuric acid are industrial waste streams that require effective management due to environmental and disposal concerns. In this study, a laboratory-scale hydrometallurgical method was developed to recover ferrous sulfate from BOF sludge using waste sulfuric acid (50% purity). The method integrates controlled acid leaching, low-temperature crystallization, and cyclic reuse of the recovered filtrate. The key features of the protocol are:•Selective acid leaching of Fe-bearing phases from BOF sludge using waste sulfuric acid at 70 °C•Low-temperature crystallization of hydrated ferrous sulfate phases at 5 °C•Cyclic reuse of the recovered filtrate to improve solution efficiencyThe protocol was validated through repeated leaching-crystallization cycles. X-ray diffraction analysis confirmed the dissolution of Fe-bearing phases from the BOF sludge and the formation of hydrated ferrous sulfate phases, including melanterite, rozenite, and szomolnokite, in the recovered products. Average ferrous sulfate yields of 8.86 ± 0.22 g, 10.10 ± 0.18 g, and 10.60 ± 0.26 g were obtained for Cycles A, B, and C, respectively, corresponding to estimated Fe recovery efficiencies of 40.2%, 46.8%, and 51.4%. These results demonstrate that the proposed method provides a reproducible route for converting BOF sludge and waste sulfuric acid into value-added ferrous sulfate while enabling filtrate reuse.