Ab initiostudy of dissolution and precipitation reactions from the edge, kink, and terrace sites of quartz as a function of pH

Abstract

In this study, the fundamental concept of mineral surface roughness and the role it plays on the dissolution and precipitation processes using ab initio density functional theory calculations, have been investigated. To understand the topological contribution to the dissolution and precipitation rates of quartz, a systematic study was designed to determine the reaction mechanisms and barrier heights of the forward reaction of hydrolysis of -Si(OH) 3 group from underlying edge, kink, and terrace sites. The edge and kink sites are topological features on mineral surfaces that are bound to the bulk with fewer Si-O-Si bridge bonds than a terrace site, a factor that can be significant in the dissolution process. In this work, the local arrangement of atoms on the underlying sites is included by systematically increasing the Si-O-Si bridging to represent the edge, kink, and terrace sites under ambient conditions in the neutral, deprotonated, and protonated states. Nine reaction profiles were studied using the M05-2X density functional with 6-31 þ G(d,p) basis set. The results show that hydrolysis of the -Si(OH) 3 group and the back reactions are not too sensitive to the underlying edge, kink, and terrace site. The barrier height data also explain the experimentally observed dissolution rate over the entire pH range, especially the tremendously high dissolution rate below pH 2.

Molecular-level mechanisms of quartz dissolution under neutral and alkaline conditions in the presence of electrolytes

“…In contrast to the neutral condition, there are now two transition states (TS1, TS2) instead of one on the pathway of the hydrolysis reactions, suggesting completely different dissolution mechanisms between the neutral and alkaline conditions. The reaction pathway profiles found here are similar to those of Xiao and Lasaga (1994) and Nangia and Garrison (2009). In Fig.…”

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…Theoretical works on the reaction of water with defects like S2R that are known to be healed in the presence of water 507,75,140 are not considered (with the exception of the SiO• species, which is a possible responsible of crystalline silicas toxicity), neither are works focusing on the first steps of silica dissolution (see refs. 501,[545][546][547][548][549] for a non-exhaustive list) that can occur for instance on rough surfaces. 547,550,551 Complex interface processes such as dissolution/precipitation and polymerisation reactions in solution 552,553 are not discussed here.…”

Probing the Mechanism of Silica Polymerization at Ambient Temperatures using Monte Carlo Simulations

“…However, ab initio calculations of condensation/hydrolysis energies for various Q i species show that these energies are remarkably uniform, roughly independent of the precise nature of reacting species. 16,17 We thus approximate the above generalized reaction (eq 1) as two hydroxyl groups reacting to form a BO and a water molecule, reducing the set of K eq to a single value. We have used K eq = 500 in this work, which gives a condensation free energy of 3.7 kcal mol -1 comparing reasonably well with the condensation energy of 3.2 kcal mol -1 obtained from density functional theory for dimerization in water.…”