Treatment of multi-dentate surface complexes and diffuse layer implementation in various speciation codes

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dc.contributor.authorLützenkirchen, Jen_AU
dc.contributor.authorMarsac, Ren_AU
dc.contributor.authorKulik, DAen_AU
dc.contributor.authorPayne, TEen_AU
dc.contributor.authorXue, ZGen_AU
dc.contributor.authorOrsetti, Sen_AU
dc.contributor.authorHaderlein, SBen_AU
dc.date.accessioned2023-09-07T01:12:13Zen_AU
dc.date.available2023-09-07T01:12:13Zen_AU
dc.date.issued2015-04en_AU
dc.date.statistics2023-07-27en_AU
dc.description.abstractSpectroscopic studies and atomistic simulations of (hydr)oxide surfaces show that ionic aqueous adsorbates can bind to one, two, three, or four surface oxygen atoms (sites), forming multi-dentate species in surface complexation reactions. The law of mass action (LMA) for such reactions can be expressed in several alternative scales of surface concentration (activity). Unlike for mono-dentate surface complexes, the numerical value of the equilibrium constant is not independent of the choice of the surface concentration scale. Here, we show in a number of examples that the different formalisms implemented in popular speciation codes (MINEQL, MINTEQ, PHREEQC, and ECOSAT) yield different results for the same systems when the same parameters are used. We conclude that it is very important to generate general equations to easily transfer stability constants between the different concentration scales. It is of utmost importance for application of these models to reactive transport that the implementation in both the model fitting and speciation codes, and in the transport codes, is transparent to users. We also point to the problem that the implementation of the diffuse layer formalism in the various codes is not necessarily generally applicable. Thus, codes like VisualMinteq or MINEQL involve the Gouy–Chapman equation, which is limited to symmetrical (z:z) electrolytes, while PHREEQC and ECOSAT use general equations. Application of the former two to environmental problems with mixed electrolytes will therefore involve an inconsistency. © 2014 Elsevier Ltd.en_AU
dc.description.sponsorshipThe authors are grateful to the sponsors and participants in the Sorption Forum of the Nuclear Energy Agency, which has facilitated the open discussion of the issues raised in this paper. Many aspects considered in this paper were discussed at the Discussion Meeting “Surface Reactions and the Electrical Interfacial Layer: Experiments and Models – Towards a Common Basis”, Opatija, Croatia, in October 2007.en_AU
dc.identifier.citationLützenkirchen, J., Marsac, R., Kulik, D. A., Payne, T. E., Xue, Z., Orsetti, S., & Haderlein, S. B. (2015). Treatment of multi-dentate surface complexes and diffuse layer implementation in various speciation codes. Applied Geochemistry, 55, 128-137. doi:10.1016/j.apgeochem.2014.07.006en_AU
dc.identifier.issn0883-2927en_AU
dc.identifier.journaltitleApplied Geochemistryen_AU
dc.identifier.pagination128-137en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15103en_AU
dc.identifier.volume55en_AU
dc.publisherElsevieren_AU
dc.relation.urihttps://doi.org/10.1016/j.apgeochem.2014.07.006en_AU
dc.subjectLayersen_AU
dc.subjectChemical stateen_AU
dc.subjectSimulationen_AU
dc.subjectEquilibriumen_AU
dc.subjectSurfacesen_AU
dc.subjectOxygenen_AU
dc.titleTreatment of multi-dentate surface complexes and diffuse layer implementation in various speciation codesen_AU
dc.typeJournal Articleen_AU
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