Phosphorus adsorption efficiency and characteristic analysis of basic oxygen furnace slag

A large amount of furnace slag is produced from steelmaking every year. The resultant by-products will severely damage the natural environment and ecosystems if not treated properly. Businesses worldwide have thus been striving for slag recycling and solving various complex problems. In this study, basic oxygen furnace slag (BOFS) was regarded as an adsorbent to adsorb phosphate in water. In addition to a physical–chemical property analysis of the by-products, the present study explored the performance of basic oxygen furnace slag in adsorbing phosphorous (P) with different size settings, and observed the surface structure of fused basic oxygen furnace slag.The results revealed that free-state Ca accounts for the majority in basic oxygen furnace slag content, demonstrating the removal of nearly all phosphorous in water. The results of Fourier-transform infrared spectroscopy (FT-IR) on basic oxygen furnace slag with >200 mesh size revealed complex wave crests at the fingerprint region (570–980 cm⁻¹). The result signifies that the basic oxygen furnace slag samples comprise strong Si─O and O─Si─O bonds within silicate minerals. Moreover, basic oxygen furnace slag samples with a particle size >200 mesh contain very high content of lime (CaO) (reaching 49.5%). This property fully demonstrates that basic oxygen furnace slag samples in a small particle size were more active as an aggregate. This study found that the Langmuir adsorption isotherm model (R² = 0.997) is slightly better than the Freundlich adsorption isotherm model (R² = 0.984), which shows that the process in which basic oxygen furnace slag adsorbs P is monolayer adsorption, and the adsorption energy is more uniformly distributed among BOFS samples. This study also found that basic oxygen furnace slag samples melted at 1200°C can effectively encapsulate some heavy metal pollutants and form stable glassy slag. The change proved that a fused basic oxygen furnace slag sample could effectively encapsulate heavy metal pollutants and formed glassy-state slag with high stability. This mechanism would reduce the likelihood of heavy metal leaching when basic oxygen furnace slag serves as a subgrade aggregate, permeable material, or concrete aggregate in the future.