Microstructure Control Effect on Crystallinity, Particle Size, and Bandgap of Ferromagnetic-AC Composites Synthesized from Nickel Slag for Industrial Waste Recycling Strategy

The sustainable recovery of valuable resources from industrial waste is a global concern, especially for nickel waste. Here, we successfully present a hydrometallurgical-thermal reduction method to convert nickel slag into functional iron-based composites. Our method involves H ₂ SO ₄ leaching and NaOH precipitation to yield a purified Fe ₂ O ₃ precursor, followed by thermal reduction at 800\(\:℃\) using activated carbon (AC) as both reductant and structural control agent. It was found that the X-ray Diffraction and Scanning Electron Microscopy confirmed the successfully phase transition from iron silicates to Fe ₂ O ₃ and demonstrate that the AC ratio critically dictates morphology, reducing the particle average size from 3.20 \(\:\mu\:\)m for initial F ₂ O ₃ to an optimal 1.6 \(\:\mu\:\)m at the 2:1 (AC: Fe ₂ O ₃ ) ratio. Fourier Transform Infrared shows the strong Fe-O bonds and confirmed the characteristic Fe ₂ O ₃ /AC interface chemistry. The 2:1 ratio produces a stable composite based on Thermal Gravimetry Analysis results and exhibits high promising functional performance, with a suitable energy gap (4.18 eV) as photocatalyst and potential ferromagnetic properties as EMI absorber.