Valorization of mill scale waste using novel deoiling methods

The steel sector is one of the leading industries in the world, but it is also highly energy- and emissions-intensive. However, the industry has been taking steps towards being more sustainable and adopting circular strategies within its processes. One of its focus areas is the reuse of its steel co-products. Mill scale is one of the more underutilized co-products due to its high oil contamination, ending up as waste for landfill disposal even if it has a high percentage of iron oxides. This study evaluates two novel treatment methods in deoiling mill scale: atmospheric pressure plasma (APP) and microwave. Three different mill scales, taken at different steelmaking stages with varying physical properties and degrees of contamination, were treated. Two of the three samples contain 4 - 5 wt% oil and 15 - 21 wt% water, while the third sample is not contaminated with oil. The results show that microwave treatment already removes all the oil contaminants at 600 W for 1 min to 3 min. APP treatment only removes moisture in the samples but not oil. Microwaved samples exhibit a change in the structural composition, with a decrease in wüstite (FeO) and magnetite (Fe3O4) content and an increase in hematite (Fe2O3) content. Plasma-treated samples do not show such changes. Overall, microwave treatment is a promising and effective technique to remove the oil contaminants from mill scale and produce a valuable iron oxide-rich material, valorizing waste into a co-product.