Dissolving silicates to build solid carbon budgets: insights from nanoscale investigations of mineral, glass, and cement interfaces
Silicate materials are widespread across natural settings and constitute key elements of sustainable materials and energy technologies. For instance, the dissolution of rock-forming silicate minerals, known as a control on the carbon cycle over geological timescales, has been identified as a key process for atmospheric carbon dioxide removal through the development of enhanced rock weathering approaches. In addition, understanding the dissolution of nuclear waste storage glass matrices or industrial byproducts such as blast furnace slags or fly ashes is crucial to evaluate the feasibility of several low-carbon emission technologies involving the development of durable nuclear waste depositories and the design of novel cements with a reduced carbon footprint.
However, state of the art knowledge on silicate material dissolution processes does not allow for reliable assessment of the weathering rates of minerals, cement and glass, thereby limiting the accuracy of the associated carbon budgets. In particular, the effect of passivation layers formed at fluid-silicate interfaces and the extrapolation of laboratory-based rates to field conditions constitute two important knowledge gaps tackled in this study.
We combined advanced experimental techniques with high-performance atomistic simulations to evaluate the impact of the formation of interfacial amorphous silica layers on silicate dissolution kinetics. Such nanoporous media were investigated in-situ using synchrotron-based grazing-incidence small-angle X-ray scattering (GISAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Furthermore, the mobility of water and alkali ions was evaluated via molecular dynamics (MD) modeling of nanoporous systems. We evaluated the ability of individual cylindrical silica nanopores to sustain concentration gradients by estimating their permeability and salt rejection capabilities.
An additional outcome of this project was the development of a new dissolution rate measurement technique, based on a coupled X-ray reflectivity (XRR) and vertical scanning interferometry (VSI) approach, delivering a relevant picture of the temporal evolution of fluid-silicate interfaces over a wider range of conditions than previously allowed.
Overall, our results open promising avenues for improved estimates of silicate dissolution rates in the field, which will serve as a basis to refined carbon budgets and associated energy strategies.