Uptake of H$^{14}$ CO$^{3-}$/$^{14}$CO$_3$$^{2−}$ by calcite: impact of ISA and chloride

The uptake of inorganic $^{14}$C (H$^{14}$CO$_3$$^−$/$^{14}$CO$_3$$^{2−}$) by calcite was investigated at pH approximate to 8.3 in the absence and presence of isosaccharinate ([ISA]tot = 10-5-0.2 M) and chloride ([NaCl]tot = 10-4-2.0 M). Calcite is representative of the last degradation stage of Portland cement, whereas ISA and chloride are components expected in low- and intermediate level short-lived waste (L/ILW-SL). A moderate $^{14}$C uptake is observed at short contact times, followed by a steady increase of the retention with time resulting in distribution ratios approximate to 103 L kg-1 at t = 60 days. This is explained by fast adsorption, followed by incorporation into the calcite structure through recrystallization phenomena. The minor impact of ISA and chloride on $^{14}$C uptake is possibly related to the formation of Ca-ISA complexes and the alteration of the surface properties of calcite. The modelling of the recrystallization process allows long-term predictions of the $^{14}$C uptake in the context of repositories for L/ILW-SL.