Dissolution of EAF slag minerals in aqueous media: Effects of sonication on brownmillerite and gehlenite

Abstract

The accumulation of electric arc furnace slag (EAFS) in landfills has been causing severe environmental problems. This study examines the dissolution properties of EAFS minerals, including brownmillerite and gehlenite, essential for their possible use in resource recovery. An investigation was conducted to compare the effects of sonication and stirring on mineral dissolution while also assessing the usage of citrate as a complexing agent for gehlenite. Synthetic brownmillerite and gehlenite minerals were dissolved in aqueous solutions at room temperature using a 1:100 g/ml ratio. The dissolved elements were measured using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), while zeta potential and X-ray Photoelectron Spectroscopy (XPS) were used to assess changes in surface chemistry. Brownmillerite had significant dissolution extents, with Al and Ca dissolving up to 16 % and 8 %, respectively, in contrast to gehlenite, which dissolved less than 2 % under similar conditions. Sonication significantly increased the dissolution of brownmillerite by up to 100 %, although its impact on gehlenite dissolution varied depending on the duration of time. Besides, adding citrate enhanced the leaching of Al and Ca from gehlenite by facilitating complexation. XPS data demonstrated differences in elemental ratios on brownmillerite and gehlenite surfaces affected by the method used and the presence of citrate. Lastly, the dissolution extents of Al and Ca from EAFS were up to 12 %, depending on time and mixing method, with a preference for sonication over stirring. In conclusion, this study showed that minerals in EAFS have distinct dissolution characteristics, and sonication and citrate can considerably enhance dissolution.