Life cycle assessment of a new pyrometallurgical approach for dezincing and valorisation of iron and steelmaking sludge in the UK

A new pyrometallurgical route enables the removal of zinc (dezincing) from iron-rich sludges from iron and steelmaking processes, allowing their reintroduction into the steel production cycle as a sinter feedstock for the blast furnace. The new technology was introduced and the life cycle assessment (LCA) was carried out to evaluate the environmental impacts arising in the treatment of seven steelmaking sludges. The technology involves preparation and roasting of sludges in a top-blown rotary converter at 1200 °C for 60 min resulting in a high degree of dezincing and retention of iron oxide. The inventory for the LCA was collected in situ and scaled up to emulate industrial conditions. The impacts were calculated for eight categories of the CML impact assessment method. The assessment determined the main environmental hotspots and compared the dezincing of sludges with the disposal to the landfill. The dezincing route was presented for the process-only burdens scenario and the avoided-burdens scenario (incorporating credits for valorisation of the dezinced product). The findings suggest that the dezincing of sludges is beneficial in majority of the impact categories compared to the landfill. On average, the dezincing results in a 9% reduction in CO<inf>2</inf> emissions, or 25% reduction when avoided burdens credits are factored in. Several process design strategies are identified to further reduce the impacts of dezincing.