Dynamics of calcium carbonate formation: geochemical modeling of a two-step mechanism

Abstract : A new kinetic model was developed based on a transition-state-theory (TST)/surface-complexation-model (SCM) coupling. It aims to describe the successive precipitation of amorphous calcium carbonate (ACC) and calcite, taking account of their mutual influence: ACC precipitates according to the standard TST and creates surface complexation sites from which calcite can form and create new surface complexation sites. When the kinetics of calcite precipitation are fast enough, the consumption of dissolved matter leads to the re-dissolution of ACC. This model is first compared to batch experiments (Gebauer et al., 2008) and then applied with a reactive transport calculation code to a dynamic experiment carried out on a microfluidic device composed of a single straight channel (Beuvier et al., 2015). The results show a good match between experiments and reactive transport modeling. This suggests that the combination of simple experimental microfluidic devices and reactive transport modeling could be a promising integrated methodology to study the dynamics of geochemical reactivity at the pore scale, as a first step before application to more complex and larger systems.