CreeS - Chromium-free Slag

The project CreeS ("Chromium-free Slag") addresses the urgent need for innovative technological solutions for a sustainable and resource-efficient production and the promotion of a circular economy. In this context, the use of production residues to reduce the CO₂ footprint of products is becoming increasingly significant. The cement industry faces the challenge of finding alternative secondary raw materials (SRM) and supplementary cementitious materials (SCM) to substitute primary raw materials and lower CO₂ emissions. 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 project CreeS develops a technological concept for producing a Cr-free StS that can be used as SRM or SCM in the cement industry. Stainless steel slags inevitably arise during stainless steel production, with limited available recycling options in Austria. The project fully exploits the potential of StS through targeted heavy metal removal and resulting material streams will be returned to the internal production cycles of the steel industry. This enables the exploration of new resource-efficient recycling pathways and significantly contributes to waste reduction and the efficient use of raw and residual materials. This approach makes an important contribution to sustainable industrial practices and the closing of material loops.

Initially, mechanical processing will be used to test the separation of Cr-containing phases. Simultaneously, Cr will be converted into water-soluble phases through oxidative thermochemical treatment and subsequently leached in a controlled process environment to produce Cr-free slag. This approach includes the injection of O₂ into the molten slag, where exothermic oxidation reactions convert Cr into its water-soluble species. The supportive influence of additives will also be investigated.

Subsequently, Cr will be leached from the StS, recovered using zero-valent iron (Fe(0)) in a fluidized bed reactor (ferroDECONT process), and fixed in a Fe-Cr hydroxide sludge. This leaching process results in Cr-free StS as well as Fe-Cr-containing sludge.

Both materials will then be assessed for their suitability for reintroduction into the cement industry (Cr-free StS) by Holcim (Österreich) GmbH and into the steel industry by Breitenfeld Edelstahl AG (Fe-Cr sludge).

The project encompasses the entire value chain: from the generation of StS to the possibilities of recovering heavy metals (particularly Cr) and producing Cr-free slag, as well as the utilization of all generated material streams. The mentioned industrial partners will be complemented by scientific partners from the Chairs for Waste Processing Technology and Waste Management, and Thermochemical Processing at Montanuniversitaet Leoben, as well as K1-Met GmbH.

This cross-system technological concept represents a significant advancement for the circular economy. The results achieved can be applied to various slag types and contribute to reducing CO₂ emissions and conserving natural resources. As a result, a positive climate contribution is achieved, creating both ecological and economic benefits.

Project lead

Dr.mont. Philipp Sedlazeck
Montanuniversität Leoben, Lehrstuhl für Abfallverwertungstechnik & Abfallwirtschaft

Project partners

• Montanuniversität Leoben Lehrstuhl für Thermoprozesstechnik (TPT)
• Breitenfeld Edelstahl Aktiengesellschaft
• ferroDECONT GmbH
• Holcim (Österreich) GmbH
• K1-MET GmbH

Dr.mont. Philipp Sedlazeck
Montanuniversität Leoben, Lehrstuhl für Abfallverwertungstechnik & Abfallwirtschaft
Franz-Josef-Str. 18, A-8700 Leoben, Austria
Tel: +43 3842 / 402-5111
E-Mail: philipp.sedlazeck@unileoben.ac.at
Web: avaw-unileoben.at