EPA LEAF Testing of a Powdered Ladle Slag to Support pH Neutralization and Stabilization/Solidification Applications

Abstract

This paper reports on the characterization of a ladle slag from an electric arc furnace (EAF) steel mill that was pulverized to enable a wide range of beneficial uses that leverage its geochemistry and strong alkaline-buffering capacity. The powdered ladle slag (PLS) was subjected to a baseline characterization and EPA 1316 (Liquid–solid partitioning as a function of liquid-to-solid ratio in solid materials using a parallel batch procedure) and EPA 1313 (Liquid–solid partitioning as a function of extract pH using a parallel batch extraction procedure) leach testing for the target analyte list (TAL) metals to successfully prequalify it for pH neutralization and stabilization/solidification applications. Its bulk chemistry and buffer capacity were consistent with those of other EAF slags and lime/cement-rich media. Mineralogically, the PLS was dominated by merwinite (approximately 15%), gehlenite (approximately 6.6%), and iron magnesium oxide (6.2%) with an amorphous (noncrystalline) content of 33%–37% and a natural pH of approximately 12.5. Most of the free lime (2.8 weight %) was associated with the amorphous phase. EPA 1316 testing indicated that all Resource Conservation and Recovery Act (RCRA) metals were at or below their reporting limits (RLs) for liquid-to-solid (L/S) ratios up to 100, except barium (Ba). For trace metals, only molybdenum (Mo) was above the RL for all L/S up to 100, whereas vanadium (V) exceeded its RL only at an L/S ratio of approximately 40. EPA 1313 leaching with sulfuric acid instead of nitric acid generally increased the concentration of all TAL metals, except for calcium and Ba. At a mid-range pH, the difference between the two acid leachates was up to four orders of magnitude for common soil minerals (e.g., aluminum), but for most others, the enhancement was about a factor of 10. For the pH range of environmental interest for stabilization/solidification applications (8–12.5), Ba, Mo, and V were the only noncommon soil mineral metals routinely detected above their respective RLs. V leaching was attributed to larnite and other silicates from a pH approximately 12.5 and increased with the pH decreasing to 10.5, thus increasing the aqueous V concentrations by a factor of 100 (to approximately 0.2 mg/L). Thereafter, V concentrations gradually became nondetectable at a range of pH 9 to pH 7.5, with karelianite (V2O4) and hydrous ferric oxides considered as the solubility-controlling phases. Overall, both EPA 1316 and EPA 1313 testing results supported the aforementioned applications.