Cesium immobilization of high pH and low pH belite-rich cement under varying temperature

Low-pH cement is being studied in radioactive waste repositories. The belite-rich cement (BRC) recently gained attention due to its higher CO2 sequestration and low pH attainment under carbonation exposure. Therefore, this study evaluated the effects of pH and temperature on cesium immobilization of BRC. High pH (12.6) and low pH (9.9) BRC were produced via air curing and carbonation treatment, respectively. The high and low pH BRC samples were placed in a leaching environment at 25 °C and 45 °C for 90 days. An inverse correlation between pH and cesium mobilization of BRC was observed. The high pH BRC achieved the lowest effective diffusion coefficient (4.05E-09 cm2/s), whereas the highest value (2.64E-07 cm2/s) was achieved in case of low pH BRC. The physicochemical and morphological properties unveiled the decrease in Si/Ca ratio of gel, precipitation of Ca2+ ions in calcite formation, and increment in pore structure connectivity (pore size > 100 nm) in low pH BRC. However, the high pH BRC demonstrated the high Si/Ca ratio in C-S-H gel, hydroxide phases and higher disconnected pores. Thermodynamic modeling revealed the presence of significant carbonated phases beyond 15% CO2 uptake. The findings contributed to the BRC’s feasibility in developing nuclear waste storage facility. [Display omitted] •Cs do not participate in compound formation with hydrated and carbonated phases.•The hydrated phases offered higher sorption sites than carbonated phases.•Increase in pore connectivity (>100 nm pore size) and Si/Ca ratio accelerate Cs mobility in low-pH BRC.•Higher leaching of Ca, Si, and Mg reduced the sorption sites for Cs in low-pH BRC.•Mobility of Cs is more sensitive to higher temperature in low-pH BRC.