Unveiling the impact of carbonation treatment on BOF slag hydration activity: Formation and development of the barrier layer

Carbonation treatment is one of the most promising methods to improve the volume stability of basic oxygen furnace (BOF) slag, but the reasons for the reduced activity of heavily carbonated BOF slag have been rarely investigated. This study prepared carbonated BOF slag under the condition of CO2 concentration at 99 % and pressure at 3.0 MPa, and evaluated its activity through various methods. The mechanism behind activity inhibition was revealed. Results showed that the maximum CO2 sequestration of BOF slag was 13.4 % within 3 h. Highly carbonated BOF slag exhibits lower hydration activity than uncarbonated slag, with a 15.9 % decrease in strength activity index and a 61.0 % reduction in cumulative hydration heat release. After carbonation treatment, a 1-5 mu m thick CaCO3 barrier layer accumulates on the surface of BOF slag, affecting slag hydration even with accelerated hydration. This barrier layer inhibits the efflux of internal calcium ions and can persist long-term during the hydration without being affected. Furthermore, carbonation treatment increased the leaching risk of heavy metal ions, particularly Mn, by 175-fold.