The mechanism of dissolution of the feldspars: Part II dissolution at conditions close to equilibrium

• We present a mechanism for the rate of dissolution close to equilibrium.
• The mechanism admits partial equilibrium.
• Data from two studies is consistent with partial equilibrium due to the removal of aluminium.
• Data from two other studies is consistent with partial equilibrium due to removal of silica.
• The mechanism predicts correct rate expressions and orders of reaction with respect to aluminium, silica and sodium.

Feldspars are one of the most common minerals on the earth's crust. The rate of dissolution of these minerals is inhibited as the concentrations of the products, particularly aluminium and silica, increase. Simple arguments based on both classical and irreversible thermodynamics fail to properly describe the experimental results. In this work, the mechanism presented in Part 1 of this series of papers is extended to account for the equilibrium conditions. The mechanism of dissolution proposed in Part 1 envisages that the reaction occurs by the parallel removal of aluminium and silica components from the surface. The parallel nature of this proposal gives rise to the possibility of partial equilibrium, due to either the removal of aluminium approaching equilibrium or the removal of silica approaching equilibrium. It is shown by the analysis presented in this paper that the available experimental data can be described by the proposed mechanism, in particular, by the phenomenon of partial equilibrium.