From Transformer Waste to Functional Substrates: Recycled Fe–Si for Sustainable Electronics

The recovery and reuse of metal-containing residues is a key strategy for advancing circular processes in sustainable electronics. In this work, Fe–Si foils recovered from discarded electrical transformers were evaluated as reusable metallic substrates with potential added-value applications. The recovered foils were subjected to a simple pre-processing route consisting of acetic acid treatment, ultrasonic cleaning, progressive sanding, and final polishing until a mirror-like surface was obtained. Structural and morphological characterization showed that the recovered material preserves the Fe crystalline structure, with the (110) identified by XRD, while SEM images revealed a clear transformation from a rough and oxidized surface to a smoother and more homogeneous finish after treatment. EDS analysis confirmed Fe as the main component, with approximately 2.16% Si, together with minor oxygen contributions associated with surface oxides. Electrical evaluation of the recovered foil showed a stable signal without significant losses from 100 Hz to 10 MHz, with a phase displacement appearing above 1 MHz, suggesting contributions from capacitive and inductive effects. These results demonstrate that transformer-derived Fe–Si residues can be upgraded through low-cost pre-processing into functional metallic substrates instead of being conventionally downcycled. The proposed approach supports circular recycling schemes by transforming electrical steel waste into reusable platforms for future conductive substrates, current collectors, shielding components, or frequency-responsive metallic supports in sustainable electronic systems.