In recent decades, increasing environmental awareness has encouraged companies to adopt more sustainable approaches and to reuse industrial waste. Iron oxide nanoparticles can be effectively applied for the adsorption of heavy metals due to their high surface activity. This study synthesized iron oxide nanoparticles from mill scale waste obtained during hot rolling of steel slabs through the sol-gel process. X-ray diffraction (XRD) analysis, using the Scherrer equation, confirmed crystallite sizes in the range of 20 to 30 nanometers, with peaks indicating the presence of magnetite (Fe₃O₄) as the primary phase. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) further verified the particle size distribution and morphology. Brunauer-Emmett-Teller (BET) analysis indicated a specific surface area of 352 m²/g for the nanoparticles, compared to 7.9 m²/g for the raw mill scale particles, while active hydroxyl groups enhanced adsorption. Adsorption experiments conducted at pH 7, with a contact time of 60 minutes and three replicates, demonstrated that up to 90% of Pb(II) and Cr(VI) could be removed with a dosage of 0.35 g of iron oxide nanoparticles in 10 mL of wastewater. The adsorption data fitted well to the Langmuir isotherm model, suggesting monolayer adsorption, and followed a pseudo-second-order kinetic model. These results highlight the potential of mill scale waste as a sustainable source for nanostructured adsorbent production, with comparisons to the literature demonstrating competitive performance.