Reactive
properties of carbonate minerals and rocks attract a significant
attention with regard to modern environmental and industrial problems,
including geologic carbon sequestration, toxic waste utilization,
cement clinker production, and the fate of carbonate shell-bearing
organisms in acidifying oceans. Despite the ultimate importance of
the problem, the number of studies connecting atomistic-scale models
to experimental observations is limited. In this work we employ the
Kinetic Monte Carlo (KMC) approach to model carbonate dissolution
at the nanometer–micron scale range and to access quantitative
relationships between the variety of surface reactive sites and experimentally
observed spatiotemporal rate variance. The presented KMC model adequately
reproduces experimentally observed dissolution patterns and rates.
We examine mechanistic and quantitative relationships between site
reactivity, atomic step velocity, etch pit evolution dynamics, and
macroscopic dissolution rates. The analysis of reactive site statistics
shows the leading role of kink sites in the control of the overall
rate. The kink site density is closely tied to the controlling types
of surface features, for example, straight and curved steps having
different structural orientations, as well as their dynamic interaction.
Structurally different kink sites and steps bring different contributions
to the total rate. The modeling results indicate that rate values
depend on the spatial distribution and the type of lattice defects.
Greatly inhomogeneous defect distribution commonly observed in natural
minerals leads to the orders of magnitude local rate variance. The
reason is in the dependence of reactive site density on the local
availability of reactive steps sources, for example, screw dislocations.
We conclude that upscaling of the atomistic models of carbonate dissolution
and macroscopic rate predictions should be done taking into account
the entire variety of reactive sites and surface features as well
as their spatiotemporal distribution.
The overall dissolution of silicate
minerals is controlled by multiple
surface reaction mechanisms, reflecting the complex structure of the
surface at both molecular- and micrometer-scale levels. This complexity
results in a large number of possible local atomic configurations
influencing site reactivity and thus a corresponding variability in
surface reactivity. The aim of this study is to elucidate the net
kinetic effect of multiple reactions taking place at the silicate–water
interface using kinetic Monte Carlo (KMC) simulations. However, achieving
the proper balance in the number of model parameters required to adequately
describe a system’s evolution versus the size of the system
can be difficult. We approach this problem through the development
of a sequence of computer models that consider details influencing
surface site reactivity. The capabilities of these models are tested
by simulating the dissolution of (001), (100), and (101) quartz faces.
Quartz is used as a representative mineral for silicate structures
because of its simple chemical composition, the availability of ab
initio calculations, and its widespread distribution in the Earth’s
crust and surface. The results show how the ability of each model
to correctly predict or reproduce experimentally observed dissolution
behavior of the quartz surface depends on model complexity, initial
surface structure, and model parametrization. The successful analysis
of mechanistic relationships between input parameters and simulation
results demonstrates the power of KMC methods in evaluating mineral
dissolution kinetics and identifying critical dissolution controls.
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