Abstract
Basic oxygen furnace (BOF) steelmaking slag is enriched in potentially toxic V which may become mobilized in high pH leachate during weathering. BOF slag was weathered under aerated and air-excluded conditions for 6 months prior to SEM/EDS and μXANES analysis to determine V host phases and speciation in both primary and secondary phases. Leached blocks show development of an altered region in which free lime and dicalcium silicate phases were absent and Ca-Si-H was precipitated (CaCO3 was also present under aerated conditions). μXANES analyses show that V was released to solution as V(V) during dicalcium silicate dissolution and some V was incorporated into neo-formed Ca-Si-H. Higher V concentrations were observed in leachate under aerated conditions than in the air-excluded leaching experiment. Aqueous V concentrations were controlled by Ca3(VO4)2 solubility, which demonstrate an inverse relationship between Ca and V concentrations. Under air-excluded conditions Ca concentrations were controlled by dicalcium silicate dissolution and Ca-Si-H precipitation, leading to relatively high Ca and correspondingly low V concentrations. Formation of CaCO3 under aerated conditions provided a sink for aqueous Ca, allowing higher V concentrations limited by kinetic dissolution rates of dicalcium silicate. Thus, V release may be slowed by the precipitation of secondary phases in the altered region, improving the prospects for slag reuse.
Highlights
Basic oxygen furnace (BOF) steelmaking is a primary method of steelmaking which accounts for ∼2/3 of worldwide steel production.[1,2] In a basic oxygen converter low carbon steel is produced by blowing oxygen through molten pig iron and recycled scrap steel to remove carbon
X-ray diffractometer (XRD) analysis showed that the slag contained Larnite, brownmillerite (dicalcium aluminoferrite; Ca2(Al, Fe)2O5), free lime (CaO), and wüstite (SI Figure S4)
The first phase had an average molar Ca/Si ratio of 2.2 ± 0.1, corresponding to the dicalcium silicate phase identified by XRD; this phase contained P, V, and trace Fe
Summary
Basic oxygen furnace (BOF) steelmaking is a primary method of steelmaking which accounts for ∼2/3 of worldwide steel production.[1,2] In a basic oxygen converter low carbon steel is produced by blowing oxygen through molten pig iron and recycled scrap steel to remove carbon. Steel slag may be enriched in phases such as free lime (CaO) and periclase (MgO) which expand on hydration, resulting in significant volume change.[11] In situations where slag cannot be reused, or where supply exceeds after-use demand, slag is generally disposed to landfill.[12]
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