title: Modeling the Adsorption of Oxalate onto Montmorillonite.
abstract: 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.
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada , Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain.
authors.forename: M Elena
authors.initials: ME
authors.lastname: Ramos
authors.affiliation: Giresun University , 28200 Giresun, Merkez/Giresun, Turkey.
authors.forename: Caglayan
authors.initials: C
authors.lastname: Emiroglu
authors.affiliation: Amphos XXI Consulting S.L., Passeig de Garcia i Faria, 49-51, E08019, Barcelona, Spain.
authors.forename: David
authors.initials: D
authors.lastname: García
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada , Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain.
authors.forename: C Ignacio
authors.initials: CI
authors.lastname: Sainz-Díaz
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada , Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain.
authors.forename: F Javier
authors.initials: FJ
authors.lastname: Huertas