Hydration Structure of the Barite (001)–Water Interface: Comparison of X-ray Reflectivity with Molecular Dynamics Simulations

Abstract

The three-dimensional structure of the barite (001)−water interface was studied using in situ specular and nonspecular X-ray reflectivity (XR). Displacements of the barium and sulfate ions in the surface of a barite crystal and the interfacial water structure were defined in the analyses. The largest relaxations (0.13 Å lateral and 0.08 Å vertical) were observed for the barium and sulfate ions in the topmost unit cell layer, which diminished rapidly with depth. The best fit structure identified four distinct adsorbed species, which in comparison with molecular dynamics (MD) simulations reveals that they are associated with positions of adsorbed water, each of which coordinates one or two surface ions (either barium, sulfate, or both). These water molecules also adsorb in positions consistent with those of bariums and sulfates in the bulk crystal lattice. These results demonstrate the importance of combining highresolution XR with MD simulations to fully describe the atomic structure of the hydrated mineral surface. The agreement between the results indicates both the uniqueness of the structural model obtained from the XR analysis and the accuracy of the force field used in the simulations.

Studies of Mineral Nucleation and Growth Across Multiple Scales: Review of the Current State of Research Using the Example of Barite (BaSO4)

“…The two surfaces are related to each other through a screw axis. Reprinted with permission from ref . Copyright (2017) American Chemical Society.…”

“…Formation of the barite (001) surface breaks three bonds to the topmost barium ion (high position, Ba high ) and one bond to the second topmost barium ion (low position, Ba low ), leaving these two ions undercoordinated with respect to their bulk coordination environments (Figure ). This leads to minor displacements of barium and sulfate groups, adsorption of water molecules, and adsorption of ions. − Water molecules adsorb directly to one or two of the surface sites, fully or partially completing the coordination shell of surface bariums (Figure ). Adsorbed waters form a primary hydration layer that is split into two distinct sublayers with a 2D density of 12.0 H 2 O/nm 2 , similar to that of other minerals such as calcite (10.9 H 2 O/nm 2 ) and muscovite (10 H 2 O/nm 2 ) .…”

Atomistics of pre-nucleation layering of liquid metals at the interface with poor nucleants

“…The inconsistency in the atomic arrangement at this interface has not been clearly explained because of the difficulty in the atomic-scale characterisation of the S/L interface both theoretically and experimentally. As an interface-sensitive, angstrom-scale resolution surface X-ray diffraction (SXRD) and X-ray crystal truncation rod (CTR) analysis has provided new insights into atomic arrangements at surfaces and interfaces 6,[25][26][27][28][29][30][31][32][33] . Compared with HRTEM, the CTR technique is a spatially averaged (~0.2 × 0.25 mm 2 in our experiment) method that can also easily distinguish the atomic species 34 .…”

Lauryl Phosphate Flotation Chemistry in Barite Flotation

“…The crystal lattice parameters of barite were taken from the American Mineralogist Crystal Structure Database [30]. The barite (001) surface was used for the lauryl phosphate adsorption simulation [31]. The pKa of lauryl phosphate is 2.85 and 7.35, respectively [29].…”