Air-Cooled Blast Furnace Slag. I: Characterization and Leaching Context

Abstract

This paper is the first in a series presenting engineering data sets that successfully supported the permit approval process in a US midwestern state bordering the Great Lakes to use air-cooled blast furnace (ACBF) slag for phosphate removal in passive stormwater runoff systems. The ACBF slag aggregates under consideration function as reactive base/subbase layers beneath porous pavement installations. Mineralogically, the ACBF slag was dominated by akermanite (Ca2MgSi2O7) and gehlenite (Ca2Al2SiO7), with a considerable amorphous phase as determined by quantitative X-ray diffraction (QXRD). ACBF slag samples taken from three different northern Indiana steel mills were tested for the United States Environmental Protection Agency (USEPA) target analyte list (TAL) metals after digestion for total content and after deionized water (DIW) leaching. Comparisons between the three strongly alkaline ACBF slags showed remarkable similarity, with many analytes below quantifiable limits due to their low levels. Synthetic precipitation leaching procedure (SPLP), toxicity characteristic leaching procedure (TCLP), and pH-dependent leaching (USEPA Method 1313) tests were also conducted. Comparisons of total content and SPLP concentrations with typical soils and soil-like media showed that the ACBF slag was often associated with a higher environmental quality. Above pH=8, the USEPA Method 1313 leaching of the Resource Conservation and Recovery Act metals was either not detected or was compliant with US federal drinking water criteria, illustrating that the naturally alkaline ACBF slag media are safe to use for passive water treatment. Moreover, acute ecotoxicity testing on ACBF slag leachates using C. dubia and P. promelas showed greater than 9% survival rate.