The Potential of Sequential Extraction in the Characterisation and Management of Wastes from Steel Processing: A Prospective Review

Abstract

As waste management regulations become more stringent, yet demand for resources continues to increase, there is a pressing need for innovative management techniques and more sophisticated supporting analysis techniques. Sequential extraction (SE) analysis, a technique previously applied to soils and sediments, offers the potential to gain a better understanding of the composition of solid wastes. SE attempts to classify potentially toxic elements (PTEs) by their associations with phases or fractions in waste, with the aim of improving resource use and reducing negative environmental impacts. In this review we explain how SE can be applied to steel wastes. These present challenges due to differences in sample characteristics compared with materials to which SE has been traditionally applied, specifically chemical composition, particle size and pH buffering capacity, which are critical when identifying a suitable SE method. We highlight the importance of delineating iron-rich phases, and find that the commonly applied BCR (The community Bureau of reference) extraction method is problematic due to difficulties with zinc speciation (a critical steel waste constituent), hence a substantially modified SEP is necessary to deal with particular characteristics of steel wastes. Successful development of SE for steel wastes could have wider implications, e.g., for the sustainable management of fly ash and mining wastes.

Keywords: chemical speciation; regulation; sequential extraction; steel wastes.

Figure 1

Crude steel produced between 1970–2013 (adapted from World steel [2]).

Figure 2

Chemical forms of metals in solid phases (Modified from [84]).

Figure 3

Relative leaching efficiency (%) of elements as a function of the final pH for MSWI (municipal solid waste incinerator) fly ash [155].