Weathering of slags

Weathering is a natural process causing the transformation of minerals, rocks, and related materials like glass under near-surface conditions. Although metallurgical slags are human-made materials, they also undergo natural weathering processes. As base metal slags weather, the released solutions may contain contaminants that could pose an environmental risk. On the other hand, weathering of ferrous slags is important because of the common reuse of the slags. This chapter summarizes factors that affect rates of slag weathering as well as defining and characterizing the two stages of weathering (incipient and advanced) as they are observed in a wide variety of individual phases and slags. We conclude that slags weather at different scales and rates depending on their chemistry and phase composition as well as the external conditions. Furthermore, weathering of slags is a process that is not perfectly reflected by natural processes because these materials are complex (in terms of texture, composition, and disequilibrium with surficial conditions) and not always analogous to rocks. Therefore, some information in this chapter on weathering is applicable to all slag types, some is relevant to only specific slag types, and some aspects require additional study.