Control of slag quality for utilisation in the construction industry (SLACON) : final report

EAF slag is a by-product of electric steelmaking, the annual quantity in Europe is around 10 M tonnes, 8 M tonnes from carbon steelmaking and 2 M tonnes from high alloyed steelmaking. The objective of this project is to increase the utilisation of EAF slag by improving the quality of this slag. The treatments investigated are during the liquid stage of the slag (optimised metallurgical process or additions or cooling procedure) and during/after solidification through water treatment (cooling/washing). As the regulations in EU countries are not uniform the slag quality classification and utilisation is based not only on the properties of the slag, but also in which country it is used. Therefore, individual solutions have to be found for each slag/ steel work. Elements such as Ba, Cr and V were successfully decreased in slag leachate to meet environmental regulations, however solutions for stabilisation of Mo and Se during the liquid stage were not found. Barium leaching was decreased with the addition of sand without increase in V leaching (the slag was slow cooled). Vanadium leaching was decreased by addition of Ca-rich material (e.g. LF slag). Chromium leaching was decreased by favouring the formation of spinels with aluminium oxide additions. In pilot scale tests with solidified slag, slag washing and water treatment with iron hydroxide adsorbent was tested. The absorbent is able to remove Mo, V and F- from slag washing water, but the solidified slag washing experiments were not yet successful in decreasing V leaching from the EAF slag.