On the Mechanism of the Dissolution of Quartz and Silica in Aqueous Solutions.

Quartz and silica are common materials, and their dissolution is of significant interest to a wide range of scientists. The kinetics of the dissolution of quartz and silica have been measured extensively, yet no clear theory of dissolution is available. A novel theory of dissolution and crystallization has recently been proposed that envisages the removal of material from the surface to form ions in solution leaving behind a charged surface vacancy. These vacancies create a potential difference across the Stern layer that accelerates or retards the removal of ions. In this way, the surface potential difference is caused by and influences the rate of the removal of ions. From this theory, a model of quartz dissolution is derived that predicts the observed orders of reaction. This prediction of the orders of reaction fits a data set consisting of 285 experiments. The model also describes the effect of Na(+), K(+), and Li(+) ions, as well as the effect of heavy water. A significant component of the model is its ability to describe the zeta potential of the quartz-water interface. The model successfully predicts a transient period at the beginning of the reaction when the rate could either increase or decrease.