Project description
In the context of an effective circular and resource-efficient economy, the use of recycled/secondary raw materials is gaining importance to reduce the carbon footprint of manufacturing industries. Lower consumption of primary raw materials conserves resources and reduces emissions from mining and subsequent processing.
With this environmental and climate objective in mind, the cement industry is seeking alternative secondary raw materials (SRM) and supplementary cementitious materials (SCM) for clinker production. Slags, particularly stainless steel slags (StS), offer large potential; however, their use has been limited due to high heavy metal contents (primarily chromium (Cr)).
The CreeS project aims to develop a technology concept for producing chromium-free StS as a case study. Depending on the phase composition, this chromium-free StS is intended to be used as SRM and, where applicable, as SCM in the cement manufacturing process.
Aims of the project
In contrast to the usual research focus of immobilising Cr in poorly soluble mineral phases, CreeS pursues an opposite approach. The slag is to be thermochemically conditioned (e.g., by injecting O2) to form water-soluble phases. The supporting effect of additives is also being investigated. Subsequently, Cr is leached from the StS, recovered using zero-valent iron (Fe(0)) in a fluidised-bed reactor (ferroDECONT process), and immobilised in an Fe–Cr hydroxide sludge. Thus, the leaching process yields a Cr-free StS and an Fe–Cr-bearing sludge.
Both materials are then evaluated for their suitability for reintroduction into industry. The Cr-free StS into the cement industry by Holcim (Austria) GmbH, and the Fe–Cr sludge into the steel industry at Breitenfeld Edelstahl AG.
In parallel, the separation of Cr-bearing phases by mechanical processing is being assessed.