HR: 0830h
AN: V11D-0531    [PDF]
TI: Monte Carlo Simulations of Feldspar Dissolution Kinetics
AU: * Zhang, L
EM: lizhang@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Luttge, A
EM: aluttge@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AB: We present a kinetic model based on Monte Carlo simulation to better understand the fundamental behavior of mineral dissolution. This model is applied to the dissolution of crystallographically defined Ca-Na feldspar surfaces. Adsorption energies of H$_{2}$O and H$_{3}$O$^{+}$ molecules to Al-O-Si and Si-O-Si bonds and activation energies to break these bonds were calculated using ab initio and DFT techniques (Xiao and Luttge, 2002). These data were obtained by taking into account both solvation effects and the immersion of molecular clusters in a dielectric continuum, i.e., water. The role of cations in the dissolution of the feldspar structure is assumed trivial and most attention is focused on the behavior of Si/Al tetrahedra. The role of the crystal structure, order/disorder phenomena, bonding characteristics of Si and Al atoms, and possible surface defects like screw dislocations and point defects are discussed. Our model allows detailed investigation of the endmembers of the plagioclase series, albite and anorthite. We analyzed the movement of steps, congruency of dissolution, inhibition, anisotropy effects, and surface composition as a function of both saturation state of the solution and crystallographic orientation of the crystal surface. Additionally, we compared the dissolution rates of albite and anorthite in the context of their ratio of Si-O-Si to Al-O-Si bonds. These results will be extended to the whole feldspar series so as to predict the fundamental behavior of feldspar dissolution and evaluate the general role of Si-O-Si and Al-O-Si bond behavior.
DE: 3947 Surfaces and interfaces
DE: 5112 Microstructure
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting