KINETICS AND MECHANISMS OF THE LABORATORY DISSOLUTION OF FELDSPARS

Abstract

The paper presents an analysis of preexisting experimental data on the kinetics and mechanism of congruent dissolution of feldspars. The analysis demonstrates that feldspar dissolution is controlled by surface reactions and proceeds in two stages: fast initial and slow final. The initial stage involves the processes of adsorption, cation exchange, and the development of a leached surface layer. These processes facilitate the access of solution components to the chemical bonds, weaken them, and thus assist in the extraction of atoms from the surface and their passage to solution. The surface complexes that control the rate of the subsequent steady-state stage may be protonized and deprotonized hydroxyl groups linked to Al and Si atoms, hydrogenous feldspar, and hydrated silica. Kinetic equations are reported that were developed for reaction mechanisms with the leading role played by the aforementioned surface complexes and describe the congruent dissolution rate (r) of feldspars in the laboratory during the steady-state stage as a function of the solution pH, temperature, feld-spar composition, solution saturation, and the concentrations of cations and organic ligands in the solution. For the simplest of these equations that most closely approximate experimental data, required coefficients for application of the equations to a numerical simulation of natural processes are reported. The advantages and disadvantages of the theoretical models utilized in the equations are analyzed, and it is demonstrated that the leading role in recent, current, and future progress in kinetic research belongs to methodical improvements.