Role of Reactive-Surface-Area Characterization in Geochemical Kinetic Models 论文

摘要

Modeling of kinetic and sorption reactions requires estimates of the surface area of natural substrates which are often difficult to measure directly. A synthesis of data indicates that BET measurements on fresh surfaces exceed geometric estimates by a mean roughness factor of 7 over a wide range in particle sizes. Surface roughness factors for naturally weathered silicates are shown to approach 200 and are strongly dependent on mineral composition. Fractal analysis indicates a dimension of 2.0, and a self similarity comparable to a smooth spherical geometry. Estimates of reactive surface areas are commonly related through transition state theory to the surface defect density. Data indicate, however, that the actual surface dislocation density is lower than commonly assumed and the number of surface dislocations that actually represent potential reaction sites must be extremely low. A compilation of available kinetic models indicates that reactive surface areas commonly are one to three orders-of-magnitude lower than physical surface areas, with closer fits for geochemical systems having short residence times.