Stability of SrCO3 within composite Portland-slag cement blends

The stability and reactivity of SrCO3 within a blended Portland-slag cement at both 20 degrees C and 60 degrees C (to simulate an indicative waste form for disposal) was determined via XRD, TG-MS, SEM-EDX and thermodynamic modelling. Sr14CO3 is a potential long-term sink for trapping radioactive 14C, produced through the nuclear fuel cycle, therefore understanding its stability in potential cementitious waste forms is of interest and importance. Incorporation of 30 wt% SrCO3 in blended Portland-slag cement caused minor reactions to occur, resulting in increased formation of carbonated AFm phases, along with stabilisation of ettringite at 20 degrees C, precluded at 60 degrees C due to the reduced stability to ettringite at this temperature. Thermodynamic modelling predicted only minor SrCO3 reactivity up to 360 days, with carbonate remaining stable over this timeframe, validated by our experimental results. Thus, thermodynamic simulations predict that SrCO3 is an effective immobilisation matrix for 14C, within a blended Portland-slag cement waste form, suitable for long-term geological disposal.

Automated summary

The stability and reactivity of SrCO3 in blended Portland-slag cement were investigated using XRD, TG-MS, SEM-EDX, and thermodynamic modelling. It was found that the addition of 30 wt% SrCO3 caused minor reactions and increased formation of carbonated AFm phases at 20 degrees C. However, at 60 degrees C, the stability of ettringite decreased and prevented its stabilization. Thermodynamic modelling showed that SrCO3 had only minor reactivity up to 360 days, and carbonate remained stable. This suggests that SrCO3 is an effective immobilisation matrix for 14C in a blended Portland-slag cement waste form suitable for long-term geological disposal.