Molecular Modeling of Phosphonate Molecules onto Barium Sulfate Terraced Surfaces

Abstract

The adsorption of phosphonate molecules onto mineral surfaces is of interest due to their use as scale inhibitors. Molecular modeling is an important tool that can aid the fundamental understanding of how these inhibitors operate. This paper presents an empirical molecular mechanics study of the adsorption of a series of straight chain phosphonate molecules onto barium sulfate. It has been found that inhibition can be predicted for this straight chain series of molecules, which differ by the number of phosphonate groups present as well as by the chain length. Even more importantly, the modeling results can predict which faces will be preferred, and this has been verified by scanning and transmission electron microscopy on the resultant barite particles. It has been found that, in general, lattice matching results in the lowest replacement energy for all of the organic molecules investigated. The agreement between the experiment and the model confirms that the dominant mechanism of interaction for the additives on barium sulfate is via the deprotonated phosphonate groups with the barium ions on the surface.

Understanding barium sulfate precipitation onto stainless steel

“…5) are the same morphology as those observed at lower temperatures [24]. These particles have been previously shown by TEM to be (100) discs [24]. Once again, the particles formed in solution (Fig.…”

“…By minimising stereochemical differences, the difference in the two additives' properties (either in inhibiting precipitation or on corrosion) mainly reflects the difference in the functionality of the inhibitors. In addition, the impact of these inhibitors on the precipitation behaviour of barium sulfate has been thoroughly investigated [23,24], thus, the effect of the substrate can be determined.…”

The interaction of EDTA with barium sulfate

“…At higher concentrations, the particles are flatter. This is also observed when barite is precipitated in the presence of a triphosphonate; in this case the flat section of the particle was shown, via selected area diffraction, to be the (100) face [9]. In the presence of EDTA this flat face was found to be the (010) (from TEM SAED shown in Fig.…”

“…Work within our group has focused on trying to understand, at a fundamental level, the interactions of inhibitor molecules with the surfaces of barium sulfate [4][5][6][7]. In addition, we have sought to take useful information from molecular modelling and see whether it correlates with inhibition and vice versa, thus undertaking several studies employing both computational and experimental techniques [8,9]. Ethylenediaminetetraacetic acid (EDTA) is a particularly interesting molecule to investigate since many consider its only action in growth inhibition experiments to be that of a complexation agent.…”

Inhibition of growth in solid solution–aqueous solution systems by non-incorporating impurities

“…Previous works have reported atomic force microscopy observations of the propagation of BaxSr1-xS04 solid solution monosteps on barite (001) surfaces [10,30]. Furthermore, it has been shown that some phosphonates are effective inhibitors of growth on barite (001) surfaces [17,18]. Therefore, future observa tions and measurements of motion of monosteps on BaxSr 1-xS04 (001) surfaces in the presence of a constant concentration of phosphonates, and for different supersaturation states (i.e.…”