Oxide nanolayer formation on surface of modified blast furnace sludge particles during voltammetric cycling in alkaline media

Knowledge of the properties of metallurgical waste is essential for the assessment of their recycling. In this work, the formation of iron oxide nanolayers during voltammetric cycling in 1 M NaOH on the particle surface of blast furnace sludge after acid leaching (BFSL) was studied. Most importantly, the effect of hydrogen on these processes was of particular interest. For these purposes, the study combines electrochemical methods, cyclic voltammetry on solid and carbon paste electrodes, with analytical optical methods (TEM). On the solid iron electrode surface as a model system, nanostructured magnetite (Fe3O4) was identified as the main oxidation product, and, to a lesser extent, also maghemite (γ-Fe203). It was found that the charges corresponding to Fe3O4 formation and its reduction together with the hydrogen evolution reaction (HER) occurring at E = − 1500 mV depend on the number of cycles and have a similar course. Additionally, in the first phase of the cycling, the accumulation of maghemite on the solid Fe-electrode surface during cycling affects the growth of the oxide layer and catalytically increases the yield of the HER. Concerning the measurement with BFSL-modified CPE, on the BFSL surface, haematite is transformed into magnetite during cycling, resulting in the same Fe3O4 nanolayer as on the solid iron electrode. In this layer, the same redox processes take place, including the influence of hydrogen in the initial stage of cycling.