Steel mill scale nanoparticles prepared via high-energy wet milling

Abstract

The environmental impact of steel production is closely linked to the large amount of waste generated by this industrial process. Mill scale, a byproduct of the hot rolling process, is typically disposed of in landfills. In this context, aiming for technological enhancement and exploring potential applications, mill scale nanoparticles were produced through high-energy wet milling. After cleaning, the waste was first dry-milled in an eccentric mill and then subjected to three sequential stages of high-energy milling with spheres of varying diameters at each stage. Variations in mill rotational speed and milling time were evaluated to achieve smaller particle sizes with minimal oxidation of the waste. Steel rolling scale predominantly contains iron, which is present as wustite, magnetite, and hematite. Particles with an average diameter of 6.26 μm, resulting from dry comminution, achieved nanometric sizes after the three stages of high-energy milling, as confirmed by transmission electron microscopy, with a specific surface area of 50.4 m²/g. The lowest tested rotational speed of 2,500 rpm and a total processing time of 13 hours were used for this. X-ray diffractograms and Mössbauer spectroscopy indicated oxidation of the material to more stable phases, such as magnetite and hematite, reducing the percentage of the wustite phase from 51.6% to 7.3%. The produced nanoparticles could serve as a promising alternative to iron-based materials, particularly in magnetic applications, such as in the biomedical field. Additionally, they may function as catalysts for wastewater treatment and have potential applications in solar energy.