Usage of BOF Slag and Next Generation EAF Slag in the Cement Industry

Two research projects examine the application of slags from today’s and future steel production in the cement industry as reactive binder components. The completed project SlagCEM investigated the recovery of iron from basic oxygen furnace (BOF) slag while simultaneously producing a clinker-like mineral product with good cementitious properties. However, a reduction of BOF slag increases its viscosity and would require unfeasible high process temperatures of > 1700 °C. Therefore, SlagCEM aimed to modify the BOF slag to reduce the viscosity to suitable ranges at treatment temperatures of approx. 1600 °C. A demonstration trial (approx. 20 tons) was carried out and the potential of the produced material as a substitute in ordinary Portland cement (OPC) was investigated. Furthermore, the environmental impact of cement production (cradle-to-gate, excluding use and end-of-life) with and without SlagCEM material was calculated via life cycle impact (LCIA). The ongoing project DRI-EOS investigates the utilization of increasing amounts of direct reduced iron (DRI)-based electric arc furnace (EAF) slag in the cement industry to compensate the reduced production of granulated blast furnace slag (GBS) being expected in the future. This requires an adjustment of the slag’s chemical composition and a rapid quenching to create an amorphous structure resulting in latent hydraulic properties. The project studies the behavior of the modified slag during the metallurgical process and during solidification, any possible negative impact on the cementitious or environmental properties as well as the potential to recover metals such as iron, chromium, manganese, vanadium, and molybdenum. The results of both projects indicate that these slags are partially suitable as reactive binders, although their performance is affected by multiple factors.