10 02 01, 10 02 02, 10 09 03

Mean from 8 samples (Zanelli et al., 2021)

In the UK, currently only around 20% of steel production is by electric arc furnace (World Steel Association, 2020), half the EU average of 40%. This is a process used predominantly for recycling scrap steel. Fluxes such as lime are added and these bond with impurities in the recycled steel to form electric arc furnace slag, EAFS. The slag contains high amounts of CaO, Fe2O3, SiO2, Al2O3 and MgO alongside the presence of other trace metals and impurities depending on the quality of the scrap steel used.

EAFS is a hard, dense material and like the other air-cooled slags considered, it is currently re-used as a construction aggregate.

Electric arc furnace slag comes from the two major electric arc furnaces of Celsa Steel in Cardiff, Liberty Speciality Steels in Rotherham and to a lesser degree Outokumpu and Sheffield Forgemasters.

There is significant scope for the volume of EAFS to increase in the future, since currently the majority of steel scrap is exported and only 23% is recycled domestically (2.6 million tonnes) (Hall, Zhang and Li, 2021). Indeed, increasing the domestic capacity for recycling steel through investment in electric arc furnaces is a significant and necessary step for the UK steel industry to move towards decarbonisation (Allwood et al., 2019)(Hall, Zhang and Li, 2021).

There are two types of slag generated through electric arc furnace process, referred to as ‘black’ and ‘white’ slag. Black slag is generated from the initial scrap melting, where lime is added and the main impurities are gathered in a foaming slag, typically containing high amounts of CaO, Fe2O3, SiO2, Al2O3 and MgO alongside the presence of other trace metals and impurities depending on the quality of the scrap steel used. White slag, also known as ladle furnace slag, is generated from the secondary refinement stage, when the molten liquid is loaded into the ladle furnace and more lime is added to remove sulphur and phosphorous (Luxán et al., 2000) (Terrones-Saeta et al., 2020). White slag has a lower content of metal oxides and a significantly higher lime content, imparting it with cementitious properties (Terrones-Saeta et al., 2020)