Iron electrowinning from a nickel refinery residue for sustainable steelmaking

Alkaline electrowinning is a promising sustainable ironmaking technology, characterised by operation at low temperatures and reduced energy consumption, in contrast to the traditional route which produces CO₂ emissions. While hematite has been the primary focus of most studies, only a limited number of alternative iron-based raw materials have been investigated as potential feedstocks for electrowinning. This work aims to evaluate, for the first time, the valorisation potential of a β-FeOOH based residue, using pretreatment-free electrowinning. The electroreduction experiments conducted in 10 M NaOH at 90°C (0.025 A.cm^-2) achieved a Faradaic efficiency of 59%, comparable to pure hematite (57%), which is traditionally regarded as a primary iron source in electrowinning for green steelmaking. Increasing the electrolyte concentration to 18 M at 105-130°C, decreased the efficiency by about 20% in comparison to hematite, revealing a lower quality of iron deposits. However, potentiostatic electrowinning in the reference conditions, -1.15 V in 10 M NaOH, successfully reached an unprecedented 83% Faradaic efficiency, accompanied by an improvement in the quality of the iron deposits. These results highlight a high potential of β-FeOOH-containing industrial residues for direct valorisation through electrowinning, contributing to a more sustainable steelmaking process.