Mitigation of alkalinity and suspended fines in steel slag leachate via CO₂ pressurization

Basic Oxygen Furnace (BOF) steel slag, a major byproduct of the steel industry, has been widely recycled for various engineering applications. Before commercialization and reuse, steel slag undergoes an aging process that involves spraying water over the stacked slag for several months in open yards to mitigate the unforeseen environmental risk. This study experimentally investigates the behavior of steel slag upon exposure to water, with particular focus on the characteristics of leachate, which are closely associated with the aging process. Two steel slag types were prepared: raw materials and those pressurized with CO₂ to promote carbonate formation via reaction with Ca²⁺. Both were packed into the column and leached with either distilled water or seawater at different flow rates. Effluent pH and turbidity were monitored over time, Also, the leachates were stirred in ambient air to allow further carbonation. Solid residues were analyzed using Scanning Electron Microscope (SEM), X-ray Energy-Dispersive Spectroscopy (EDS), and Thermogravimetric Analysis (TGA). Pressurizing steel slag with CO₂ was found to reduce leachate pH, while turbidity was primarily attributed to suspended carbonate particles. Flow rate had a negligible effect, whereas seawater interaction induced a turbidity rise.