『Abstract
With previous two-dimensional (2D) simulations based on surface-specific
feldspar dissolution succeeding in relating the macroscopic feldspar
kinetics to the molecular-scale surface reactions of Si and Al
atoms (Zhang and Luttge(uの頭に¨), 2008, 2009),
we extended our modeling effort to three-dimensional (3D) feldspar
particle dissolution simulations. Bearing on the same theoretical
basis, the 3D feldspar particle dissolution simulations have verified
the anisotropic surface kinetics observed in the 2D surface-specific
simulations. The combined effect of saturation state, pH, and
temperature on the surface kinetics anisotropy has been subsequently
evaluated, found offering diverse options for morphological evolution
of dissolving feldspar nanoparticles with varying grain sizes
and starting shapes. Among the three primary faces on the simulated
feldspar surface, the (100) face has the biggest dissolution rate
across an extensively wide saturation state range and thus acquires
a higher percentage of the surface area upon dissolution. The
slowest dissolution occurs to either (001) or (010) faces depending
on the bond energies of Si-(O)-Si (ΦSi-O-Si/kT)
and Al-(O)-Si (ΦAl-O-Si/kT). When the ratio
of ΦSi-O-Si/kT to ΦAl-O-Si/kT
changes from 6:3 to 7:5, the dissolution rates of three primary
faces change from the trend of (100)>(010)>(001) to the rend of
(100)>(001)>(010). The rate difference between faces becomes more
distinct and accordingly edge rounding becomes more significant.
Feldspar nanoparticles also experience an increasing degree of
edge rounding from far-from-equilibrium to close-to-equilibrium.
Furthermore, we assessed the connection between the continuous
morphological modification and the variation in the bulk dissolution
rate during the dissolution of a single feldspar particle. Different
normalization treatments equivalent to the commonly used mass,
cube assumption, sphere assumption, geometric surface area, and
reactive surface area normalizations have been used to normalize
the bulk dissolution rate. For each of the treatments, time consistence
and grain size dependence of the normalized dissolution rate have
been evaluated and the results revealed significant dependences
on the magnitude of surface kinetic anisotropy under differing
environmental conditions. In general, the normalized dissolution
rates are strongly dependent on grain size. Time-consistent normalization
treatment varies with the investigated condition. The modeling
results suggest that the sphere-, cube-, and BET-normalized dissolution
rates are appropriate under the far-from-equilibrium conditions
at low pH where these normalizations are time-consistent and are
slightly dependent on grain size.』
1. Introduction
2. Kinetic model
2.1. 2D surface-specific kinetic anisotropies
2.2. 3D feldspar particle dissolution
3. Results and discussion
3.1. Anisotropic surface kinetics and processes
3.1.1. Anisotropic surface kinetics
3.1.2. ΦSi-O-Si vs. ΦAl-O-Si
3.1.3. Anisotropic surface processes
3.1.4. The bulk dissolution rate
3.2. 3D simulations associated with feldspar particle dissolution
3.2.1. Morphological evolution of feldspar particles
3.2.2. Layer-retreat velocities of specific faces
3.2.3. Saturation state dependence
3.2.4. Size dependence of morphological evolution
3.3. Dissolution rate normalization
4. Conclusions
Acknowledgments
Reference