Free Energy of Adsorption of Water and Metal Ions on the {101̄4} Calcite Surface

Abstract

We calculated the free energy profiles of water and three metal ions (magnesium, calcium, and strontium) adsorbing on the [1014] calcite surface in aqueous solution. The approach uses molecular dynamics with parametrized equations to describe the interatomic forces. The potential model is able to reproduce the interactions between water and the metal ions regardless of whether they are at the mineral surface or in bulk water. The simulations predict that the free energy of adsorption of water is relatively small compared to the enthalpy of adsorption calculated in previous papers. This suggests a large change in entropy associated with the water adsorption on the surface. We also demonstrate that the free energy profile of a metal ion adsorbing on the surface correlates with the solvent density and that the rate of formation of an innersphere complex depends on overcoming a large free energy barrier, which is mainly electrostatic in nature. Furthermore, comparison among the rates of desorption of magnesium, calcium, and strontium from the calcite surface suggests that magnesium has a much lower rate of desorption due to its strong interactions with both water and the surface.

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

“…Polycarboxylic acids are known to strongly complex Ca 2+ and to lesser extent Na + ions [48][49], which could result in a reduction of the capacity of the additive to bind to the surface. The second reason may be the highly layered structure of water found above a calcite surface with regions of alternating low and high water density [40,50]. As the additive backbones are hydrophobic, the molecules will have a tendency to stay in low density water regions, which are known from both experiment [50] and simulations [40] to be located roughly at 2.8 Å and 3.9 Å from the surface.…”

“…The water potential is that of de Leeuw and Parker [39] with the added hydrogen bonding modification of Kerisit and Parker [40]. Calcite-water and sodium ion-water interactions are described using the potentials of Kerisit and Parker [40] and Spagnoli et al [41].…”

“…Calcite-water and sodium ion-water interactions are described using the potentials of Kerisit and Parker [40] and Spagnoli et al [41]. The intra-additives and additive/water term were taken from the DREIDING [42] organic force-field together with the potentials derived by Duffy and Harding [26] for stearic acid, which has the same functional groups, in order to describe the interaction between the mineral and the polymer.…”

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

“…In support of this inference, molecular dynamics (MD) simulations of barium sulfate growth suggest that the kinetics of Ba 2+ attachmentwhich govern barite nucleation and growth (20)-may be ratelimited by the partial desolvation of the metal to form an innersphere surface complex (21). Likewise, experimental (22,23), theoretical (13,24), and molecular simulation studies (25) suggest that the kinetics of metal attachment at calcite surfaces may be related to the dehydration frequency of the metal near the surface. More broadly, the rate constants of several metal ligandexchange reactions [Mg and Ni binding to a range of organic ligands (26,27), the dissolution of orthosilicate minerals containing a range of divalent metals (28,29)] have been shown to correlate with the water-exchange rates of metals in liquid water, k wex (the inverse of the residence time of water in the first solvation shell of the metal).…”

Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

“…This last observation engendered a large number of ancillary studies on silica, clay, and calcite/water interfaces and their ion-exchange behavior, especially recently (Lager et al 2008a;Sorbie and Collins 2010;Nasralla and Nasr-El-Din 2012;Alotaibi et al 2011;Alotaibi and Yousef 2015;Alshakhs and Kovscek 2015;Brady Myint and Firoozabadi 2015;Puntervold et al 2015;Qiao et al 2016). Fundamental studies (Ricci et al 2013;Alshakhs and Kovscek 2015;Brady et al 2015;Lashkarbolooki et al 2016;Mugele et al 2016) of the calcite/water interface, including molecular simulation (Kerisit and Parker 2004;Sakuma et al 2014;Qiao et al 2016), also garnered attention. These results generally support the surface-charge-recovery concepts of DLE and MIE.…”