Electric arc furnaces allow steel mills to produce steel from a 100% scrap metal feedstock, rather than from iron ore and coal used in the blast furnace steelmaking method. EAFs use electricity and emit significantly less carbon dioxide than blast furnaces. Slag is the rock-like material by-product that forms from the lower density materials during the steel smelting process. This EAF slag goes through crushing and screening processes to recover any iron pieces, followed by iron purification and alloying in secondary and tertiary ladle furnaces.
In a new study, researchers wanted to determine if this by-product could serve some new, innovative and beneficial use. One challenge is that EAF steel mill size affects the quantity of slag aggregates that can be stockpiled, and transportation costs limit the shipping distance 50-100 miles, making older metropolitan areas potential candidates based on need and reuse opportunities. Their paper “EPA LEAF Testing of a Powdered Ladle Slag to Support pH Neutralization and Stabilization/Solidification Applications,” reports on the select material properties and leaching behavior of powdered ladle slag. PLS material is ideal for large-scale cement-based applications and potentially a substitute for portland cement. The authors selected New Jersey as their reference basis due to the number of environmental stabilization/solidification projects and stabilized dredged material processing and then prequalified the PLS media against regional environmental regulations. Ideally to be of beneficial use, industrial by-products must not contribute to current levels of site contamination and perform similarly to materials they are replacing. Learn more about this research in the Journal of Hazardous, Toxic and Radioactive Waste at https://doi.org/10.1061/JHTRBP.HZENG-1209. The abstract is below.
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.
See if you can think of uses for this pulverized slag in the ASCE Library: https://doi.org/10.1061/JHTRBP.HZENG-1209.
