『Abstract
In natural weathering systems, both the chemistry and the topography
of mineral surfaces change as rocks and minerals equilibrate to
surface conditions. Most geochemical research has focused on changes
in solution chemistry over time; however, temporal changes in
surface topography may also yield information about rates and
mechanisms of dissolution. We use stochastic dissolution simulations
of a regular 2-D lattice with reaction mechanisms defined in terms
of nearest neighbor interactions to elucidate how the surface
area and reactivity of a crystal evolve during dissolution. Despite
the simplicity of the model, it reproduces key features observed
or inferred for mineral dissolution. Our model results indicate
that : (i) dissolving surfaces reach a steady-state coformation
after sufficient dissolution time, (ii) linear defects cause surface
area and dissolution rate to vary in concert with one another,
(iii) sigmoidal and non-sigmoidal rate vs. free-energy of reaction
(ΔGrxn) behavior can be rationalized in terms
of the multiple steps occurring during dissolution, and (iv) surface
roughness as a function of is ΔGrxn is highly
sensitive to the reaction mechanism. When simulated times to reach
steady-state are compared to published time series rate data using
suitable scaling, good agreement is found for silicate minerals
while the model significantly over-predicts the duration of the
transient for Fe and Al oxides. The implication of our simple
model is that many aspects of mineral dissolution behavior, including
approach to steady-state, sigmoidal vs. non-sigmoidal rate vs.
ΔGrxn behavior, and development of rougher
surfaces in conditions further from equilibrium can be explained
by nearest neighbor interactions and simple Kossel-type models
where reactivity of a surface is defined in terms of perfect surface,
step, and kink sites.』
1. Introduction
2. Approach
2.1. Model description
2.2. Simulation methods
3. Results
3.1. Steady-state exists over a broad range of dissolution
mechanisms
3.2. Effect of defects on the existence of a steady-state
3.3. Effect of ΔGrxn on steady-state rate
and surface area
4. Discussion
4.1. Steady-state dissolution
4.2. Weak influence of defects on surface area normalized dissolution
rate
4.3. Controls on the existence of an inflection point in dissolution
rate vs. ΔGrxn
4.4. Mechanistic implications of decreasing roughness
as a function of ΔGrxn
5. Conclusions
Acknowledgments
Appendix A
Appendix B. Supplementary data
References