Impact of Pore-Scale Processes on Silicate Dissolution Kinetics

The rates and mechanisms associated to the dissolution of silicate materials including minerals, glasses, and cements have been a prominent concern over the past 50 years in a range of fields. In particular, silicate alteration rates have important implications for the long-term carbon cycle at the global scale and the feasibility of several low-carbon energy technologies including green cements, carbon capture and storage, and radioactive waste storage. Fundamental controls on the rates of silicate weathering remain incompletely understood, especially due to silica-rich nanoporous coatings forming at reacting interfaces, which have been shown to strongly modulate the alteration rate of the underlying solid. Here we suggest that a key to the impact of silicate alteration layers lies in their analogy to systems such as semi-permeable membranes or nanofluidic diodes. We investigated the mobility of water and alkali ions through single cylindrical silica nanopores with the LAMMPS code. Our simulations used the CLAYFF model in combination with the extended simple point charge (SPC/E) water model to build a relevant water-silica-ions system including the effect of negative surface charge. We determined the permeability and salt rejection capabilities for single silica pores with varying diameters and surface charge densities. We showed that such systems developed highly remarkable properties because of a combination of Coulomb and steric interactions with the pore walls, which may explain the particular behavior of silica nanopore networks that constitute silica-rich interfacial layers. Overall, our approach will contribute to better understand pore-scale processes and to develop more consistent descriptions of the transport properties at the interface between reacting fluids and dissolving silicates in the Earth's Critical Zones and deeper subsurface environments.