Use of Basic Oxygen Furnace (BOF) Steel Slag for Acid Mine Drainage Treatment: A Laboratory Study

Abstract

We investigated the feasibility of using alkaline basic oxygen furnace (BOF) steel slag to treat acid mine drainage (AMD). Simulated AMD was treated with different doses of slag (10, 20, 30, 40, 50, and 60 g/L) for 24 h in batch reactors. A dose of 30 g/L was considered optimal because it raised the pH to 8.6 and resulted in 99% removal of trace metals in 24 h. The pH increased to 6.36 from the initial pH of 1.5 within 0.5 h of reaction time. Approximately 95% of all trace metals were removed. Of the major cations and anions, Mg showed the highest percentage removal (72%), followed by SO4 (30%), K (8%), and Na (2.1%) at the 30 g/L dose and 0.5 h reaction time. However, Ca concentrations increased by 28% due to leaching from the slag. PHREEQC was used to predict the possible mineral phases precipitating during treatment. Calculated saturation indices indicated that Fe was removed mainly as goethite, hematite, and amorphous Fe(OH)3; Al was removed as gibbsite and amorphous Al(OH)3; Mn was removed as manganite, hausmannite, and pyrolusite; Mg was removed as Mg(OH)2; and Ca and SO4 were only minimally controlled by gypsum precipitation. Moreover, sulfate removal was increased by the precipitation of alunite, an Al-oxy hydroxysulfate mineral. Other trace elements were either co-precipitated with or adsorbed onto the Fe, Al, and Mn precipitates. Field emission scanning electron microscope analysis of the slag after interaction with the AMD revealed that metals and SO4 precipitated on the slag surface.