Assessment of valorisation opportunities for secondary metallurgy slag through multi-criteria decision making

This paper aims to investigate the valorisation opportunities for the secondary metallurgy slag (SMS) as a by-product of electric arc furnace (EAF) steel production. The key stakeholders, their aim and possible configurations of the SMS value chain are identified considering the treatment unit owners and locations, pre-treatment and treatment processes, and collaboration aspects. A multi-criteria Analytic Hierarchy Process (AHP) model has been developed to evaluate value chain configurations according to criteria such as technology, legislation, economic and environmental sustainability, and supply chain. This approach helps analyse the impact of circular economy practices and the opportunities for industrial symbiosis in the European steelmaking areas. The AHP model was tested on the case of Lombardy region that is one of the major European hubs for EAF steel production. Knowledge was collected and formalized from interviews with several experts. The results show economic sustainability has the highest impact on the SMS value chain, followed by CO2 emission and water consumption. The ranking of SMS value chain configurations shows that a pre-treatment phase is essential since it facilitates SMS logistics management and has environmental advantages. A collaborative approach among steel producers or with external recyclers is preferred when there is the readiness of the ecosystem, hardware infrastructure, and legislation about product certificates and operations. In a collaborative system, a value chain consisting of a third-party industry for SMS recycling is preferred to a consortium of producers due to the broader market coverage, environmental sustainability, and higher profits for the recycler. The multi-criteria combined with the multi-expert modelling approach helps balance the importance of different criteria from the actors' points of view, such as steel producers and technology providers. From the theoretical point of view, the analysis shows how an SMS collaborative ecosystem integrated with two recycling facilities reinforces the steelmaking business profitability, market potential, and environmental-friendly solutions. This study can help steel producers decide on the feasibility and profitability of treatment units, collaborating with other producers, or selling SMS to recyclers. In addition, policymakers can analyse the regional perspective, identify potential industrial sectors, and explore new business models.