Microwave-induced modifications in electric arc furnace slag: An attempt to enhance aqueous dissolution

Electric arc furnace slag (EAFS) is produced in large amounts during steel manufacturing and can pose ecological hazards when disposed of in nature. Its heterogeneity, intricate mineralogy, and low solubility restrict its applicability in numerous fields, such as cementitious binders, resource recovery, and mineralization. This study investigated three different microwave irradiation techniques—direct (MWD), roasting with NaOH (MWR), and solution (MWS)—to modify the EAFS and exceed the current boundaries. The former involved direct exposure of EAFS (D90: <30 μm) to microwaves, while the latter included a mixed of EAFS and NaOH, followed by microwave roasting. Both microwave-irradiated samples were later dissolved via stirring in aqueous conditions at a 1:100 g/mL ratio. In contrast, MWS comprised dissolution of EAFS in water under microwave irradiation in a closed vessel. The elemental releases were then analyzed using an inductively coupled plasma-optical emission spectrometer. Structural, surface chemistry, and morphology examinations were also conducted. The results indicated that the structural alterations directly influenced release of Al, leading to a dissolution extent of 25 % for MWR, in contrast to the reference, which attained only 10 %. The release of Si was only achieved using MWR, reaching 3 %. The release of Ca was prominent in the MWS, achieving the highest concentration relative to the others and exhibiting 50 % enhancement. The findings obtained by surface and solution chemistry and microstructural images supported the differences in elemental releases among sample series following microwave irradiation. In conclusion, this study demonstrated the promising potential of microwave irradiation to enhance the dissolution of EAFS, providing more insights into its appropriate applications and valuable reuse. • Microwave irradiations – direct, roasting, and solution – were applied to enhance the dissolution of EAFS. • Al, Si, Ca, and Mg were released in aqueous conditions with varying concentrations, depending on the microwave irradiation. • Microwave roasting achieved the highest Al releases with a dissolution extent of 25 %. • Microwave irradiation in solution resulted in a 50 % increase in Ca release compared to reference stirring.