Application of a novel miniaturized counter diffusion cell for deriving time and space-resolved dynamics of CaCO3 precipitation in silica gel via coupled micro-XRF/XRD and SAXS imaging.
E001
Abstract
Geochemical processes like mineral precipitation and dissolution in confined spaces continuously modify the natural properties of porous systems such as rocks, aquifers, sediments, or soils. Yet, these systems’ small space (nanometer to micrometer) scale hinders the quantification of critical dynamical processes and features (e.g., nucleation pathways, polymorph type, crystal morphology, nucleation pathways) controlling mineral precipitation in porous media. An additional difficulty is continuously monitoring such phenomena over the long timescale of their evolution. Nevertheless, the quantitative experimental derivation of the process parameters is imperative for validating pore-scale reactive transport models. In this study, we overcome limitations by developing a novel miniaturized counter diffusion cell setup consisting of a 300 µm glass capillary filled with silica gel connected to reservoirs containing CaCl2 and Na2CO3 solutions on the opposite ends. The system was monitored continuously through optical microscopy. At selected time points, XRF/XRD chemical imaging and SAXS measurements were carried out to reflect the different precipitation stages and the geometry of clogging zones. Thus, these data allowed the quantification of nucleation times and local growth kinetics of the different CaCO3 polymorphs formed (vaterite, calcite, aragonite, and amorphous CaCO3) in Silica-gel. When analyzed using recent developments related to non-classical nucleation theory, these datasets have allowed us to systematically assign the dependency of pH and supersaturation on the nucleation probability of vaterite and calcite polymorphs.