Pore-scale characterization of transverse mixing-induced calcium carbonate precipitation of relevance to geological carbon sequestration

This study examines the reaction between carbonate and calcium to precipitate calcium carbonate in an experimental model. This model is a small micro-fluidic device that incorporates a flow channel with an imprinted homogeneous pore structure to replicate the porous nature of groundwater flow. Sodium carbonate and calcium chloride were injected in to this model to form a calcium carbonate precipitate. The experiment was run and analyzed visually as well as analytically with tools including light, laser confocal, and Raman spectroscopy. The main points of interest include the morphology of the crystals and the rates of crystal formation. A thin line of calcium carbonate formed in the model composed of coarse calcite crystals and fine vaterite crystals. At lower concentrations, this precipitate line was more irregular, wider, and contained more calcite crystals; as concentration increased, the precipitate line became straighter, thinner, and contained more vaterite. Also, precipitation occurred more quickly with increasing concentration. A better understanding of precipitation reactions is important to determine the challenges associated with geological carbon sequestration