Effects of magnesium ions on near-equilibrium calcite dissolution: Step kinetics and morphology

Xu, Man; Higgins, Steven R.

doi:10.1016/j.gca.2010.10.018

Cited by 40 publications

(28 citation statements)

References 48 publications

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“…The second is an actual relationship with X c through surface poisoning. Chemisorption of magnesium onto calcite could either prevent other species from attacking the mineral surface, or prevent steps from retreating (Xu and Higgins, 2011). If magnesium were the cause of our observed criticality, this would imply that at seawater Mg concentrations (53 mmol/kg), X c must shift towards equilibrium.…”

Section: The Nonlinearity Of Calcite Dissolution In Seawatermentioning

confidence: 90%

“…There is evidence that Hg 2þ does not appreciably adsorb onto calcite (Bilinski et al, 1991), and thus should not interfere with dissolution kinetics. There is also some evidence that magnesium ion could play a role in inhibiting step edge formation and propagation close to equilibrium (Xu and Higgins, 2011). These authors report an inhibitory effect at X c = 0.2, although their X is poorly constrained due to gas exchange considerations.…”

Section: The Nonlinearity Of Calcite Dissolution In Seawatermentioning

confidence: 99%

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A novel determination of calcite dissolution kinetics in seawater

Subhas

Rollins

Berelson

et al. 2015

Geochimica et Cosmochimica Acta

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Section: The Nonlinearity Of Calcite Dissolution In Seawatermentioning

confidence: 90%

Section: The Nonlinearity Of Calcite Dissolution In Seawatermentioning

confidence: 99%

A novel determination of calcite dissolution kinetics in seawater

Subhas

Rollins

Berelson

et al. 2015

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

“…Evidence for this concept the observation that various surface sites have varying equilibrium constants and formation energies despite being predicted from models that include the solubility product as a term in the lattice enthalpy to which the model was calibrated . Coupled to this is experimental evidence of non‐zero step advance/retreat rates under nominally equilibrium solution, a phenomenon not allowed in this model. A second potentially problematic assumption in Eqn is that it requires a one‐dimensional critical nucleus to form prior to kink propagation becoming thermodynamically stable.…”

Section: The Next Generation Of Modelsmentioning

confidence: 99%

“…Under saturation indices > 0.4, the best fit model for Eqn contains a negligible detachment . This action is justified by observations of calcite dissolution in which impurities only inhibit growth above a threshold undersaturation, SI ≥ –0.7, but below which attachment is negligible . This has not been tested during calcite growth, but some atomic force microscopy data taken as a function of saturation state suggests a change in slope of the growth rate at SI ≅ 0.2 (recalculated as saturation index relative to a K sp = 10 −8.…”

Section: The Next Generation Of Modelsmentioning

confidence: 99%

“…28 Th is action is justifi ed by observations of calcite dissolution in which impurities only inhibit growth above a threshold undersaturation, SI ≥ -0.7, but below which attachment is negligible. 55 Th is has not been tested during calcite growth, but some atomic force microscopy data taken as a function of saturation state suggests a change in slope of the growth rate at SI ≅ 0.2 (recalculated as saturation index relative to a K sp = 10 -8. 48 ), 54 possibly suggesting that the back reaction for growth is only signifi cant below that saturation index.…”

Section: The Next Generation Of Modelsmentioning

confidence: 99%

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Next generation models of carbonate mineral growth and dissolution

Stack

2014

Greenhouse Gas Sci Technol

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The long-term success of carbon sequestration lies in part on the ability to trap carbon dioxide as a carbonate mineral phase. As such, the ability to predict the extent of carbonate mineral precipitation over the lifetime of a proposed geologic sequestration site will be necessary. In this review, different methods of predicting the growth of carbonate minerals, particularly calcite, and their disadvantages and advantages are summarized. Starting from a simple description of the solution saturation state, more advanced affi nity-based models are described that comprise the status quo. In these, the reaction rate is measured by the difference in concentration from an equilibrium value or the Gibbs Free Energy of reaction. It is shown that these models fail to capture some important aspects of carbonate mineral growth rates. Next-generation models in development are those that refl ect the processes that occur on a mineral surface while it is growing, not just the concentration of dissolved species. While incomplete, these process-based models are already addressing some long-standing questions in geochemistry and are enhancing the accuracy and robustness of the predictive ability for calcite precipitation. Lastly, the importance of the step density, analogous to the reactive site density in a natural sample, is shown. The factors that may infl uence the step density are described and the potentially complex relationship between step density and solution conditions is presented. While still in development, these models suggest that many of the historical problems in quantitative prediction of mineral growth and dissolution reactions can be resolved.

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Biosorption of copper using nopal fibres: moolooite formation and magnesium role in the reactive crystallization mechanism

et al. 2020

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In this contribution, we present findings on biosorption of Cu (II) ions using novel alkali-treated nopal fibres. The biosorption data at equilibrium were fitted to several isotherm models and the biosorbent was characterized by XRD and SEM–EDX. The biosorption mechanism was investigated using a holistic approach of pH shifts, apparent colour variations and changes in the concentration of Cu(II) and dissolved hard ions (calcium and magnesium) in the Cu(II) solution. The correlation between the colour, XRD analysis, pH shifts and hard cations released from the biosorbent into the solution suggested the existence of two crystal formations, malachite and moolooite, in what appears to be a microprecipitation mechanism via reactive crystallization. The role of magnesium during the transformation of malachite into moolooite during the copper binding mechanism is analysed. Magnesium cations were released into the solution during malachite growth but were taken up from the solution during the moolooite crystal growth phase. The shift of the molar ratio Mg/Ca was located between the two inflexion points of the crystal growth transition. This specific location at the sorption isotherm was correlated with the colour evolution by a linear discriminant model confirming its association with the polymorphs. Graphic abstract

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Effects of magnesium ions on near-equilibrium calcite dissolution: Step kinetics and morphology

Cited by 40 publications

References 48 publications

A novel determination of calcite dissolution kinetics in seawater

A novel determination of calcite dissolution kinetics in seawater

Next generation models of carbonate mineral growth and dissolution

Biosorption of copper using nopal fibres: moolooite formation and magnesium role in the reactive crystallization mechanism

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