Kinetics of montmorillonite dissolution

Ramos, M. Elena; García-Palma, Susana; Rozalén, Marisa; Johnston, Cliff T.; Huertas, F. Javier

doi:10.1016/j.chemgeo.2013.11.014

Cited by 35 publications

(19 citation statements)

References 64 publications

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“…This study uses the Integrated Massively Parallel Atmospheric Chemical Transport (IMPACT) model (Rotman et al, 2004;Liu et al, 2005;Feng and Penner, 2007;Ito et al, 2007Ito et al, , 2012Ito et al, , 2015Lin et al, 2014;Xu and Penner, 2012;Ito, 2015). The model is driven by assimilated meteorological fields from the Goddard Earth Observation System (GEOS) of the NASA Global Modeling and Assimilation Office (GMAO).…”

Section: Model Descriptionmentioning

confidence: 99%

Delivery of anthropogenic bioavailable iron from mineral dust and combustion aerosols to the ocean

Ito¹,

Shi²

2015

Preprint

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Abstract. Atmospheric deposition of anthropogenic soluble iron (Fe) to the ocean has been suggested to modulate primary ocean productivity and thus indirectly affect the climate. A key process contributing to anthropogenic sources of soluble Fe is associated with air pollution, which acidifies Fe-containing mineral aerosols during their transport and leads to Fe transformation from insoluble to soluble forms. However, there is large uncertainty in our estimate of this anthropogenic soluble Fe. Here, we, for the first time, interactively combined laboratory kinetic experiments with global aerosol modeling to more accurately quantify anthropogenic soluble Fe due to air pollution. We firstly examined Fe dissolution kinetics of African dust samples at acidic pH values with and without ionic species commonly found in aerosol water (i.e., sulfate and oxalate). We then constructed a new empirical scheme for Fe release from mineral dust due to inorganic and organic anions in aerosol water, by using acidity as a master variable. We implemented this new scheme and applied an updated mineralogical emission database in a global atmospheric chemistry transport model to estimate the atmospheric concentration and deposition flux of soluble Fe under preindustrial and modern conditions. Our improved model successfully captured the inverse relationship of Fe solubility and total Fe loading measured over the North Atlantic Ocean (i.e., 1–2 orders of magnitude lower Fe solubility in North African- than combustion-influenced aerosols). The model results show a positive relationship between Fe solubility and water soluble organic carbon (WSOC)/Fe molar ratio, which is consistent with previous field measurements. We estimated that deposition of soluble Fe to the ocean increased from 0.05–0.07 Tg Fe yr−1 in preindustrial era to 0.11–0.12 Tg Fe yr−1 in present days, due to air pollution. Over the High Nitrate Low Chlorophyll (HNLC) regions of the ocean, the modeled Fe solubility remains low for mineral dust (< 1 %) in a base simulation but is substantially enhanced in a sensitivity simulation, which permits the Fe dissolution for mineral aerosols in the presence of excess oxalate under low acidity during daytime. Our model results suggest that human activities contribute to about half of the soluble Fe supply to a significant portion of the oceans in the Northern Hemisphere, while their contribution to oceans in high latitudes remains uncertain due to limited understanding of dust Fe dissolution under pristine conditions.

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Section: Model Descriptionmentioning

confidence: 99%

Delivery of anthropogenic bioavailable iron from mineral dust and combustion aerosols to the ocean

Ito¹,

Shi²

2015

Preprint

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“…Adsorption Experiments. In this study, we used adsorption data previously reported by Ramos et al 1 For the sake of clarity, the experimental information that is relevant to this data is briefly provided.…”

Section: Methodsmentioning

confidence: 99%

“…Moreover, special attention was focused on making sure that the final model was in good semiquantitative agreement with previously reported FTIR spectroscopic measurements. 1 2.4. Computational Methodology and Atomistic Models.…”

Section: Aloh Alo Hmentioning

confidence: 99%

“…15−25 In the present work, the adsorption of oxalate at the edge surface of montmorillonite has been successfully modeled on the basis of results from previous investigations. 1 The results of this study allow one to make quantitative predictions that can facilitate evaluation of the potential role of mineral surface chemistry in several geochemical processes involving the interactions of organic molecules and mineral surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…In a previous study, diffuse reflectance Fourier-transform infrared (DR-FTIR) spectroscopy was used to identify the types of oxalate surface complexes on the montmorillonite surface. 1 However, due to the limited amount of oxalate sorbed, it was difficult to make a statement about the type of complexes formed. The quantitative adsorption was also studied at different oxalate concentrations.…”

Section: Introductionmentioning

confidence: 99%

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Modeling the Adsorption of Oxalate onto Montmorillonite

et al. 2015

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In this work, a multiscale modeling of the interaction of oxalate with clay mineral surfaces from macroscale thermodynamic equilibria simulations to atomistic calculations is presented. Previous results from macroscopic adsorption data of oxalate on montmorillonite in 0.01 M KNO3 media at 25 °C within the pH range from 2.5 to 9 have been used to develop a surface complexation model. The experimental adsorption edge data were fitted using the triple-layer model (TLM) with the aid of the FITEQL 4.0 computer program. Surface complexation of oxalate is described by two reactions: >AlOH + Ox(2-) + 2H(+) = >AlOxH + H2O (log K = 14.39) and >AlOH + Ox(2-) + H(+) = >AlOx(-) + H2O (log K = 10.39). The monodentate complex >AlOxH dominated adsorption below pH 4, and the bidentate complex >AlOx(-) was predominant at higher pH values. Both of the proposed inner-sphere oxalate species are qualitatively consistent with previously published diffuse reflectance FTIR spectroscopic results for oxalate on montmorillonite edge surface (Chem. Geol. 2014, 363, 283-292). Atomistic computational studies have been performed to understand the interactions at the molecular level between adsorbates and mineral surface, showing the atomic structures and IR frequency shifts of the adsorption complexes of oxalate with the edge surface of a periodic montmorillonite model.

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