Mineralogical approaches to fundamental crystal dissolution kinetics - Dissolution of an A3B structure

Abstract

Incorporating mineral structures and interpreting the wide array of water-rock kinetic field and experimental data, requires abandoning molecule-based adsorption phenomenological models and the development and analysis of a general kinetic theory that incorporates all the basic processes occurring in the destruction of a crystal structure. The current paper extends our prior work to include an analysis of the kinetic behavior of an A 3 B-type crystal structure. More complex kink types and two different bonding energetics for A-A and A-B bonds add new kinetic phenomena during dissolution. The rate laws for both perfect and stepped surfaces are contrasted and compared to simple TST-like rate laws. Unexpected changes in mechanism as a function of saturation state are found and studied. Incongruent dissolution is analyzed as a function of time and saturation state. The appropriateness of additive rate laws for various reaction mechanisms is investigated using the mechanism change from step-control to hole-nucleation control for A 3 B structures. The onset of inhibition, predicted by the statistical mechanical treatment of the kinetics, is observed as conditions far from equilibrium are reached. Inhibition is quantified with the use of isotachs and it is seen to depend systematically on the average surface bonding properties. In particular, a quantification of the number of B vacancies with saturation state is carried out and compared with actual results from the full kinetic model. The analysis of the inhibition mechanism itself and its onset are then applied to analyze recent feldspar dissolution data.