Structure and Surface Complexation at the Calcite(104)–Water Interface

Abstract

Calcite is the most stable polymorph of calcium carbonate (CaCO3) under ambient conditions and is ubiquitous in natural systems. It plays a major role in controlling pH in environmental settings. Electrostatic phenomena at the calcite–water interface and the surface reactivity of calcite in general have important environmental implications. They may strongly impact nutrient and contaminant mobility in soils and other subsurface environments, they control oil recovery from limestone reservoirs, and they may impact the safety of nuclear waste disposal sites. Besides the environmental relevance, the topic is significant for industrial applications and cultural heritage preservation. In this study, the structure of the calcite(104)–water interface is investigated on the basis of a new extensive set of crystal truncation rod data. The results agree with recently reported structures and resolve previous ambiguities with respect to the coordination sphere of surface Ca ions. These structural features are introduced into an electrostatic three-plane surface complexation model, describing ion adsorption and charging at the calcite–water interface. Inner surface potential data for calcite, as measured with a calcite single-crystal electrode, are used as constraints for the model in addition to zeta potential data. Ion adsorption parameters are compared with molecular dynamics simulations. All model parameters, including protonation constants, ion-binding parameters, and Helmholtz capacitances, are within physically and chemically plausible ranges. A PhreeqC version of the model is presented, which we hope will foster application of the model in environmental studies.

Laboratory Measurements of Zeta Potential in Fractured Lewisian Gneiss: Implications for the Characterization of Flow in Fractured Crystalline Bedrock

“…For details, refer to the cited papers. The data sources are: a-Vinogradov et al [31]; b-Walker and Glover [32]; c-Jaafar et al [42]; d-Vinogradov et al [43]; e-Vinogradov and Jackson [44]; f-Li et al [45]; g-Tosha et al [35]; h-Reppert and Morgan [46]; i-Morgan et al [47]; j-Ishido and Mizutani [48]; k-Al Mahrouqi et al [34]; l-Jackson et al [49]; m-Collini et al [50]; n-Heberling et al [51]; o-Heberling et al [52]. [31]) and carbonates saturated with equilibrated NaCl solutions [34] are shown in green and black dashed lines, respectively.…”

Ordered and Disordered Carboxylic Acid Monolayers on Calcite (104) and Muscovite (001) Surfaces

“…When looking at the specular rod in more detail, we observe a sharp minimum in the structure factors around a value of 5 for diffraction index in both cases, which is not present in the calcite−water system. 24,35 Besides this, there is strong experimental 15 and theoretical evidence 14,36−38 for the adsorption of short-chain carboxylic acids on the (104) calcite surface. The nonspecular crystal truncation rods look more similar to those of the calcite−water system, 24 which is an indication of laterally disordered carboxylic acid molecules.…”

Retention of Iodide by Chloride Green Rust and Magnetite

“…To model the ion-exchange reaction, two half-reactions were defined (eqs and ), which sum up to the overall ion-exchange process (eq ). The overall affinity of iodide to exchange for chloride in the GR structure, log­( k s ) as defined by eq , was adjusted to obtain an optimal fit between data and model . The individual constants for the half-reactions (eqs and ) are arbitrary (i.e., one is defined relative to the other): …”

“…25 The overall affinity of iodide to exchange for chloride in the GR structure, log(k s ) as defined by eq 5, was adjusted to obtain an optimal fit between data and model. 27 The individual constants for the half-reactions (eqs 2 and 3) are arbitrary (i.e., one is defined relative to the other):…”