Soft Matter and Complex Systems Seminar

Interface-coupled dissolution and precipitation (ICDP) processes control the evolution of reactive mineral/fluid systems in many subsurface environments, from CO₂ sequestration and concrete carbonation to steel corrosion in nuclear waste repositories and natural hydrogen generation. ICDP involves the dissolution of a primary mineral and the precipitation of a secondary phase directly on its surface, forming a rim. This rim may facilitate complete replacement of the parent phase or lead to passivation or mineral armoring. Despite its importance, the mechanisms governing mineral passivation and the fate of co-evolving gas phases remain poorly understood.
To address these gaps, we combined controlled column and microfluidic experiments with advanced microstructural characterization and pore-scale modelling. Using a model system which is redox- and pH-insensitive with the primary mineral celestine (SrSO4) covered with secondary barite (BaSO4), we quantified the role of barite nucleation dynamics, barite porosity, and the heterogeneity of celestine surface reactivity in driving mineral armoring. Three-dimensional FIB-SEM and HAADF-STEM analyses revealed nanoporosity in the secondary barite rim, while microfluidic experiments coupled with in-situ Raman and AFM imaging demonstrated how spatial variations in surface reactivity govern localized dissolution–precipitation patterns. Pore-scale modelling further showed that selective ion diffusion and electric double layer effects contribute to mineral passivation.
We extended this framework to ICDP systems involving gas generation. Using witherite (BaCO3) dissolution in sulfate-rich acidic solutions, we observed that the concomitant precipitation of barite and CO₂ exsolution forms distinctive “cauliflower-like”, mineral precipitates encrusting gas bubbles. These textures arise from electrostatic enrichment of ions around gas bubbles, promoting barite nucleation and trapping water droplets within mineral shells. When precipitation outpaces dissolution, these structures inhibit further mineral reaction and clog pore spaces, potentially impeding CO₂ storage, hydrogen recovery, and metal corrosion processes.
Together, our results reveal the coupled roles of surface chemistry, microstructure, and fluid dynamics in controlling ICDP kinetics and the evolution of reactive interfaces, key to predicting the long-term reactivity and permeability of subsurface systems.