Abstract
There is a pressing need for innovative waste management approaches as environmental regulations become more stringent worldwide alongside increasing demand for a more circular economy. Sequential chemical extraction (SE) analysis, which has previously been applied to environmental media such as soils and sediments, offers the potential to provide an understanding of the composition of solid steel processing by products, aiding the waste classification process and improving environmental protection. The definition of seven-phase associations through a SE method evaluated in this study were for (1) water soluble, (2) ion exchangeable, (3) carbonate, (4) amorphous Fe–Mn oxides, (5) crystalline Fe–Mn oxides, (6) sulphides and (7) silicate residues. Steel waste by-products (flue dust and filter cake) were evaluated for both extracted components (ICP analysis) and residual phases (using powder X-ray diffraction, SEM and FTIR), to model the transformations taking place during extraction. The presence and removal of important potentially toxic element (PTE) host solid phases were confirmed during extraction. The SE protocol provides key information, particularly for the association of potentially toxic elements with the first three extracts, which are most sensitive in waste management processes. The water-soluble phase is the most available followed by ion-exchangeable and carbonate fractions, all representing phases more sensitive to environmental change, in particular to pH. This study demonstrates that the distribution of potentially toxic elements such as zinc, lead and copper between sensitive and immobile phases can be reliably obtained in technological process by-products. We demonstrate that despite heterogeneity as a major variable, even for fine particulate matter, SE can provide more refined classification with information to identify reuse potential and ultimately minimise hazardous waste streams.
Highlights
Waste management regulations worldwide are becoming more stringent, and the option to landfill wastes is being increasingly reduced (CEWEP 2012; Cointreau 2008; World Steel Association 2014)
We focus on the following potentially toxic elements (PTEs) of particular interest: Cr, Cu, Mn, Pb and Zn
This study has confirmed that the application of a sevenstep sequential extraction method for steel industry process by-products provides phase association data for potentially toxic elements of environmental and process concern
Summary
Waste management regulations worldwide are becoming more stringent, and the option to landfill wastes is being increasingly reduced (CEWEP 2012; Cointreau 2008; World Steel Association 2014). Industrial operators from steel production or mining are faced with a critical need to assess their waste generation and the sustainability of current production processes. The amount of waste being generated can corrupt the production process infrastructure and can cause environmental damage and breach regulatory thresholds. This adds to financial operating costs and causes. The opportunity to learn more about elemental associations supports the development of sustainable processes and a more circular economy within the steel industry: through stabilisation and reclassification of commercially valuable elements which could be re-used within the production line, reducing waste and costs to an industrial operation
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