High-temperature slag engineering in pursuit of effective mineral carbonation of pyroxene-rich ferronickel slag

The search for resources for low-carbon construction materials and valorization pathways for industrial residues go hand in hand. Mineral carbonation has been abundantly studied to strive for a net-zero CO₂ construction sector. Ferronickel slags have been studied for the production of other cementitious materials, but have inferior carbonation potential due to their low Ca-content. This work shows that the reactivity of a pyroxene-rich ferronickel slag towards CO₂ can be substantially increased using high-temperature slag engineering. Using a combination of CaCO₃ additions and slow cooling, the produced compacts made from synthesized slags acquire a compressive strength of 30–40 MPa after carbonation at 10 bar CO₂ and 60 °C for 16 hours. The reactivity towards CO₂ originates from the formation of akermanite (Ca₂MgSi₂O₇) during slag modification with > 20 wt% CaCO₃. The compressive strength is dependent on the particle size distribution of the modified slag and carbonation time. Although the reaction degree of akermanite is high after 6 hours of carbonation, a significant strength increase is still seen after carbonation for 16 and 48 hours. The carbonation process forms a binding phase composed of aragonite and a CaMg-carbonate which might be high Mg-calcite or protodolomite. The CO₂ balance of the overall process shows a substantially lower value compared to Portland clinker-based cements, but additional efforts are required to develop an optimum net-zero CO₂ process.