Effects of Pore-Scale Heterogeneity and Solution Chemistry on Transverse Mixing Induced Calcium Carbonate Precipitation

Mineral precipitation limited by advective or diffusive mixing in porous media is relevant to several processes in the subsurface, these include precipitation near the injection well and fringes of the plume during i) carbon sequestration, ii) groundwater remediation, and iii) precipitation of leachate along the shadow zones of nuclear waste storage. In our previous work, microfluidic pore network structures etched into silicon substrate were used as model subsurface sedimentary system to study coupled processes of advection, diffusion and calcium carbonate precipitation at the pore-scale. It was found that, counter-intuitively, less precipitates were formed in the mixing zone between calcium chloride and sodium carbonate at higher solution saturation sates, due to pore blockage and reduced mixing by precipitates, which also slowed the phase transformation process. To further expand this work, additional experiments were carried out to investigate effects of pore-scale heterogeneity, competing ions (e.g., magnesium), and ionic strength on mixing induced calcium carbonate precipitation. The primary interests are how these factors affect the reaction rates, morphology, phases and stability of the precipitates, and impacts on porosity and effective permeability.