Simulation of surface dynamics during dissolution as a function of the surface orientation: Implications for non-constant dissolution rates

Abstract

Available online xxxx Editor: J. Brodholt Keywords: modeling kinetics rate constant topography dissolution surfaceAn important problem in geochemistry is the understanding of how changes occurring on a surface during dissolution affect the variability of measured dissolution rates. In this study a new approach to study the effect of surface dynamics on dissolution rates is tested by coupling experimental data with a numerical model that simulates the retreat of surface profiles during dissolution. We present specific results from the simulation of dissolution of fluorite surfaces. The equations that determine the retreat of a surface are based on experimentally obtained equations that relate the retreat rate of a surface to a single variable, the crystallographic orientation of the surface. Our results show that depending on the starting orientation, different types of topography are developed, similar to those observed experimentally. During the initial dissolution phase, changes of topography are rapid and associated with fast dissolution rates. The progressively slower dissolution rates are coupled with the development of surface segments with orientations that dissolve at a slower rate. Consequently, the overall retreat rate of a profile decreases during the simulation, and tends to a near-constant value. The results show a close relationship between dissolution rates, surface orientation and surface dynamics, which suggests that the dissolution rate of a specific mineral phase is not constant but varies with dissolution time and surface structure. This variability needs to be considered in the evaluation of experimentally derived dissolution rates, future dissolution experiments, and predictive kinetic models of dissolution.

Comparing the reactivity of glasses with their crystalline equivalents: The case study of plagioclase feldspar

“…Recent studies showing that the structural anisotropy of a mineral induces changes in terms of surface area and reactivity during the dissolution process are nice illustrations of this assertion (Bandstra and Brantley, 2008;Daval et al, 2013;Godinho et al, 2014a, Gruber et al, 2014Pollet-Villard et al, 2016a, b). The demonstration of the impact of various energy surface sites (dislocations, kink and step sites for minerals, differently coordinated Si surface groups for glasses) on dissolution rates is also a good example (Dove et al, 2008;Fischer et al, 2014;Pollet-Villard et al, 2016;Godinho et al, 2014a). Finally, the potential passivating role of surface layers developed during the weathering process has been shown as crucial for both crystalline and amorphous silicate structures (Casey, 2008;Gin et al, 2015;Hellmann et al, 2015;Gin et al, 2018).…”

“…As dissolution progresses, the density of steps should decrease, exposing larger areas of more stable planes, characterized by a lower surface energy. Such observations have been made in several studies on the dissolution of fluorite (Godinho et al, 2013;Godinho et al, 2014a;Godinho et al, 2014b;Maldonado et al, 2013) and calcite (Smith et al, 2013), coupling experimental surface retreat data with the simulation of dissolution of a selection of crystal surfaces. This scenario is consistent with the obtained results for albite crystal, which…”

“…The progressive evolution of the surface area during the dissolution process and the impact of these physicochemical changes on dissolution rates should be taken into account to develop more realistic dissolution models (Lüttge et al, 2013). Recent studies showing that the structural anisotropy of a mineral induces changes in terms of surface area and reactivity during the dissolution process are nice illustrations of this assertion (Bandstra and Brantley, 2008;Daval et al, 2013;Godinho et al, 2014a, Gruber et al, 2014Pollet-Villard et al, 2016a, b). The demonstration of the impact of various energy surface sites (dislocations, kink and step sites for minerals, differently coordinated Si surface groups for glasses) on dissolution rates is also a good example (Dove et al, 2008;Fischer et al, 2014;Pollet-Villard et al, 2016;Godinho et al, 2014a).…”

A Statistical Approach for Analysis of Dissolution Rates Including Surface Morphology

“…Nevertheless, experiments with well-defined extrinsic parameters and statistical analysis of results provide important clues for defining the intrinsic parameters. As discussed by previous authors [17,38,44,[46][47][48], this effort can only be achieved with the combined effort of numerical modelling studies. The highest frequency dissolution rates reported here (e.g., Figure 7a) are in the same order of magnitude as reported in other VSI and AFM studies [18,22,49].…”

A review of numerical modelling of the dynamics of microstructural development in rocks and ice: Past, present and future

“…Here, we present a numerical model that simulates the dissolution process as a potential tool to quantify the links between dissolution rates, reactive surface area and topography over periods of time beyond reasonable for a laboratory experiment. The program uses empirical equations that relate the dissolution rate of a point of the surface with its crystallographic orientation(Godinho et al, 2012) to simulate changes of topography during dissolution, which ultimately results in the variation of the overall dissolution rate(Godinho et al, 2012(Godinho et al, , 2014. The initial surface is composed of a group of nodes with a xy position and a set height (z).…”