Molecular simulation and microtextural characterization of quartz dissolution in sodium hydroxide
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ORIGINAL PAPER-EXPLORATION GEOLOGY
Molecular simulation and microtextural characterization of quartz dissolution in sodium hydroxide Abdullah Musa Ali1 · Noorhana Yahya2 · Abubakar Mijinyawa1 · Mohammed Yerima Kwaya1 · Surajudeen Sikiru2 Received: 10 January 2020 / Accepted: 20 June 2020 © The Author(s) 2020
Abstract This study uses empirical experimental evidence and Material Studio simulations to explain the interaction of sodium hydroxide (NaOH) with quartz. Density functional theory (DFT) calculations were carried out using the Cambridge Serial Total Energy Package. In addition, quartz grains subjected to dissolution in NaOH were characterized using scanning electron microscopy. The so-called O-middle termination in the quartz tetrahedron structure, typified by a solitary exposed oxygen atom at the surface, is the most susceptible S iO2 terminations to NaOH attack, as it is associated with the lowest surface energy. The adsorption energy values are − 1.44 kcal/mol and − 5.90 kcal/mol for a single atom layer and five-layered atomic structure, respectively. The DFT calculation reveals intramolecular energy is the dominant adsorption energy, followed by a weak van der Waals energy. The NaOH adsorbed on quartz (001) surface constitutes a lower band gap of 0.138 eV compared to cleaved quartz (001) surface (0.157 eV). In addition, the energy range of NaOH adsorbed on quartz is wider (− 50 to 10 eV), compared to (001) quartz (− 20 to 11 eV). The dissolved quartz showed the precipitation of sorbed silicate phases due to incongruent reactions, which indicates new voids and etch pits can be created through the cleaving of the sodium silicates sorbed into the quartz surface. The adsorption energy for NaOH interactions with reservoir sandstone was significantly higher compared to the solitary crystal grains, which can be attributed to the isotropic deformation of a single crystal, and non-uniform deformations of adjacent grains in granular quartz of sandstone reservoir. It can be inferred that exposure to NaOH will affect the structure and reactivity of quartz. The quartz surface textural study indicates that dissolution of crystalline (granite) and clastic rocks (sandstone) is critical to the development of voids, which will improve permeability by providing channels and routes for the passage of hydrothermal and reservoir fluids. Keywords Quartz dissolution · Sodium hydroxide (NaOH) · Absorption energy · Density of states · Microtextural features
Introduction Quartz is an abundant silicate mineral that plays a significant part in geological studies, as oxygen and silicon are the key elements of Earth’s crust. Understanding the kinetics of quartz–water reaction is critical in elucidating a number of important topics in geochemistry such as soil formation and degradation, chemical weathering, enhanced porosity in reservoirs via dissolution and C O2 * Abdullah Musa Ali [email protected] 1
Department of Geology, Bayero University Kano (BUK), Kano, Nigeria
Fundamental and Applied Sciences Department, Univers
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