『Abstract
Determining the kinetics of many geologic and engineering processes
involving solid/fluid interactions requires a fundamental understanding
of the Gibbs free energy dependency of the system. Currently,
significant discrepancies seem to exist between kinetic datasets
measured to determine the relationship between dissolution rate
and Gibbs free energy. To identify the causes of these discrepancies,
we have combined vertical scanning interferometry, atomic force
microscopy, and scanning electron microscopy techniques to identify
dissolution mechanisms and quantify dissolution rates of albite
single crystals over a range of Gibbs free energy (-61.1<ΔG<-10.2
kJ/mol). During our experiments, both a previously dissolved albite
surface exhibiting etch pits and a pristine surface lacking dissolution
features were dissolved simultaneously within a hydrothermal,
flow-through reactor. Experimental results document an up to 2
orders of magnitude difference in dissolution rate between the
differently pretreated surfaces, which are dominated by different
dissolution mechanisms. The rate difference, which persists over
a range of solution saturation state, indicates that the dissolution
mechanisms obey different Gibbs free energy dependencies. We propose
that this difference in rates is the direct consequence of a kinetic
change in dissolution mechanism with deviation from equilibrium
conditions. The existence of this kinetic “switch” indicates that
a single, continuous function describing the relationship between
dissolution rate and Gibbs free energy may be insufficient. Finally,
we discuss some of the potential consequences of our findings
on albite's weathering rates with a particular focus on the sample's
history.』
1. Introduction
2. Materials and methods
2.1. Materials
2.2. Solution saturation states
2.3. Reactor descriptions
2.4. Dissolution rate measurements
2.5. Atomic force microscopy and scanning electron microscopy
3. Results
3.1. Temperature dependency of albite dissolution rates
3.2. Gibbs free energy dependency of albite dissolution rates
and mechanisms
3.2.1. Dissolution rates
3.2.2. Etch pit densities
3.2.3. Etch pit morphologies
4. Discussion
5. Implications for natural and experimental systems
6. Summary and conclusions
Acknowledgments
Appendix A
References