Clay Amendment for pH Mitigation of Electric Arc Furnace Ladle Slag

Steel slag is obtained as a byproduct of the steel industry and corresponds to approximately 15%-20% of each ton of steel slag produced by weight. When steel is produced in an electric arc furnace (EAF) where high-power electric arcs substitute gaseous fuels for heat production, the molten steel may be subjected to a second-stage process for further refinement, such as desulfurization or nitrogen removal; after this process, the lightweight material floating on the ladle above the purified steel is called ladle slag (EAFLS). Due to the addition of different alloys in the secondary refinement, EAFLS has a slightly different chemical composition than EAF slags. Particularly, the alkaline nature of the material due to the addition of purifying agents results in a high pH of the leachate along with excessive trace metal concentrations, which consequently leads to potential harm to human health and aquatic species. Thus, a comprehensive evaluation of the chemical properties of ladle slag along with potential mitigation techniques might be necessary to assess its suitability from a geo-environmental point of view. In this study, a series of batch water leach tests (WLT) were performed to investigate the environmental impacts of ladle slag (EAFLS) utilization in geotechnical engineering applications. The chemical composition and mineralogical properties of the material were determined via X-ray fluorescence spectrometry (XRF) and X-ray diffraction (XRD) analyses, respectively. Moreover, slag was mixed with different amounts of clayey subgrade soil by weight to examine the efficiency of clay amendment as a method to mitigate high alkalinity and toxic trace elements released. The results indicate that EAFLS contains a significant amount of calcium and magnesium, which confirms the high alkalinity of the material. Increasing clay percentage within the slag-clay mixture results in a considerable decrease in pH, electrical conductivity (EC), and total dissolved solids (TDS) of the leachate, which also shows that due to its negative surface charge by nature, clay amendment can be used as a treatment alternative.