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

Abstract

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.

Extending Surface‐Enhanced Raman Spectroscopy to Liquids Using Shell‐Isolated Plasmonic Superstructures

“…Note that the bare, primary amine-, and thiol-functionalized SiO 2 spheres all show as trongly fluctuatingz eta potential at pH > 10.5 due to dissolution of SiO 2 . [25] The SiO 2 -PEI spheres do not display these fluc-tuations,i ndicating that the polymer completely coverst he SiO 2 surface, preventing direct contact with the medium. At pH < 8.5, the surfacec harge of SiO 2 -NH 2 spheres starts to deviate from the behavior exhibitedb yb are and thiol-functionalized SiO 2 spheres, while the latter two show nearly identical behavior,i ndicating that silanol groups dominate the charge on the surface as hinted upon in the Ramans pectrum of SiO 2 -SH in Figure 1d.J udging on the behavior of the surface charge of SiO 2 -NH 2 spheres above pH 8.5, these particles also exhibit silanol groups alongside the primary amines.…”

“…Figure e summarizes zeta potential measurements of all the SiO 2 spheres over the pH range 1–12. Note that the bare, primary amine‐, and thiol‐functionalized SiO 2 spheres all show a strongly fluctuating zeta potential at pH >10.5 due to dissolution of SiO 2 . The SiO 2 ‐PEI spheres do not display these fluctuations, indicating that the polymer completely covers the SiO 2 surface, preventing direct contact with the medium.…”

Ionic Diffusion, Nanoparticle Formation and Trapping Within Sol‐Gel Made Pillared Planar Nanochannels in a Simple Microfluidic Device

“…Thus, if a partially dehydroxylated surface is exposed to basic water it will have a larger number of silanol groups in respect to a surface that is only exposed to neutral or slightly acidic water . This has consequences in the following discussion as a different number of silanol group on the silica surface influences its surface charge and its interaction with water . During operation, diffusion of the solutions into the PPN brings both reactants towards one another.…”

“…[69] This has consequences in the following discussion as a different number of silanol group on the silica surface influences its surface charge and its interaction with water. [70,71] During operation, diffusion of the solutions into the PPN brings both reactants towards one another. Precipitation of black Ag (reaction reported in equation (10) [72] with A corresponding to the hydrazine and silver corresponding to B of equation (1))…”

Improved parameterization of the weathering kinetics module in the PROFILE and ForSAFE models

“…A formulation based on transition state theory for the formation of activated surface complexes that decay irreversibly was developed by (Sverdrup 1985, Sverdrup and Warfvinge 1987, 1988a,b, 1992, Sverdrup 1990 to describe the effect of dissolved metals on primary mineral dissolution at far from equilibrium conditions. Taking account of this approach as well as their coupling to solute transport, ion exchange, plant nutrient uptake, organic matter decomposition and nitrogen transformations detailed modelling of chemical weathering rates have been made (Sverdrup and Warfvinge 1988a,b, Sverdrup 1990, Akselsson et al, 2006, 2004, 2017. A comparison of calculated and observed weathering rates shown in Figure 2, demonstrates this approach can reproduce the observed rates within ±5% across 4 orders of magnitude for the upper unsaturated parts of a soil , Barkman et al, 1999, Belyazid 2005, Kurz et al, 1998a.…”