Dissolution kinetics of quartz in sodium chloride solutions: Analysis of existing data and a rate model for 25°C
Abstract
A surface reaction model for the kinetics of quartz dissolution is derived from an analysis of lowtemperature dissolution rate data published by seven experimenters. The model correlates seventynine quartz dissolution rate measurements with calculated surface species distributions to predict reaction kinetics. Using the triple layer electrostatic surface model, we compute the distributions of predominant acidbase surface species for the solution composition associated with each reported rate measurement. Reactivities of the modeled species are then obtained by fitting the calculated site distributions and the experimental rate data to a simple rate equation. This results in an expression valid for 25°C, pH 213 and 00.5 molal sodium chloride given by rate = 10 ^{13.0}(θ _{SiOH}∗ + 10 ^{10.8}(θ _{SiOsum}) ^{1} + 10 ^{9.2}(θ _{SiOsum}) ^{2}, where rate has units of mol m ^{2}s ^{1},θ _{4;SiOH} is the fraction of SiOH surface complexes and ∗ indicates that the reaction order dependence on this species is illdetermined. The θSiOsum term gives the sum of SiONa ^{+} and SiO ^{} fractions. This correlation removes much of the apparent scatter that is observed between experimenters and demonstrates that most measurements follow a consistent trend when a sodium complex, SiONa ^{+}, is included in the model. The model predicts that reaction rates are increased by a factor of 12 at pH 8 with the addition of 0.2 molal sodium to the reacting solutions. While this approach is an indirect measure of the reactivity of bonds at mineral surfaces, when compared to previous models, it offers a better understanding of ratecontrolling processes because it specifically includes the calculated distributions of surface reactants. This analysis, in conjunction with evidence from the literature for cationspecific influences on silicon dioxide reactivity, supports a dissolution model incorporating cation interactions.
 Publication:

Geochimica et Cosmochimica Acta
 Pub Date:
 December 1992
 DOI:
 10.1016/00167037(92)90257J
 Bibcode:
 1992GeCoA..56.4147D