Adsorption of Organic Matter at Mineral/Water Interfaces:  3. Implications of Surface Dissolution for Adsorption of Oxalate

Abstract

The adsorption of oxalate on a model aluminum oxide, corundum (alpha-Al2O3), has been examined over a broad range of oxalate concentrations (0.125-25.0 mM) and pH conditions (2-10). In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) measurements indicate that at low to intermediate concentrations ([oxalate] < or = 2.50 mM), oxalate adsorbs to corundum predominantly as a bidentate, mononuclear, inner-sphere complex involving both carboxyl groups. Significant contributions from outer-spherically bound oxalate and aqueous Ox(2-) are additionally observed at higher oxalate concentrations. Consistent with the ATR-FTIR findings, macroscopic adsorption data measured for oxalate concentrations of 0.125-2.50 mM can be generally well modeled with a single bidentate, inner-sphere oxalate complex using the charge distribution multisite complexation (CD-MUSIC) model. However, at intermediate oxalate concentrations (0.50 and 1.25 mM) and pH <5, the extent of oxalate adsorption measured experimentally is found to fall significantly below that predicted by CD-MUSIC simulations. The latter finding is interpreted in terms of competition for oxalate from dissolved Al(III), the formation of which is promoted by the dissolution-enhancing properties of the adsorbed oxalate anion. In accordance with this expectation, increasing concentrations of dissolved Al(III) in solution are found to significantly decrease the extent of oxalate adsorption on corundum under acidic pH conditions, presumably through promoting the formation of Al(III)-oxalate complexes with reduced affinities for the corundum surface compared with the uncomplexed oxalate anion.

Mineral Surfaces, Geochemical Complexities, and the Origins of Life

“…Dozens of recent studies reveal complexity in structure and speciation of adsorbed organics, particularly through in situ FTIR and other spectroscopic studies (Somasundaran and Krishnakumar 1994;Rodriguez et al 1996;Holmen et al 1997;Roddick-Lanzilotta et al 1998;Fitts et al 1999;Klug and Forsling 1999;Kubicki et al 1999;McQuillan 1999, 2000;Duckworth and Martin 2001;Sheals et al 2002;Lackovic et al 2003;Rosenqvist et al 2003;Yoon et al 2004Yoon et al , 2005Johnson et al 2004aJohnson et al , 2004bJohnson et al , 2004cJohnson et al , 2005aJohnson et al , 2005b (Thomas et al 1993;Orme et al 2001;Asthagiri and Hazen 2007). In addition, for the calcite-water interface, many theoretical simulations and observations exist to guide surface chemical models (Stipp and Hochella 1991;Parker 1997, 1999;Teng et al 1998Teng et al , 2000Fenter et al 2000;Wright et al 2001;Stipp 2002;de Leeuw and Cooper 2004;Geissbuhler et al 2004;Kristensen et al 2004).…”

Effect of carboxylic and thiol ligands (oxalate, cysteine) on the kinetics of desorption of Hg(II) from kaolinite

“…These play an important role in aquatic and soil chemistry (Biber and Stumm 1994). Numerous studies have been reported on the adsorption of these organic acids on clay minerals and metal oxides Dzombak 1998 andFilius et al 1997;Horanyi 2002;Johnson et al 2004;Kang and Xing 2007;Kirwan, et al 2003;Xu and Ji 2003). The present study can also help to reveal the role of the LMM OAs in the environmental chemistry of Hg.…”

“…A competition thus occurs between particles and NOM for binding Hg(II) (Arias et al 2004;Singh et al 1996). NOM can also bind to particles (Johnson et al 2004;Schuster 1991) and affect Hg(II) distribution between particles and solutions. Particle-ligand-Hg(II) thus forms an interesting ternary system in aquatic systems and soils.…”

Mineral-Aqueous Solution Interfaces and Their Impact on the Environment

“…ATR-FTIR is arguably the spectroscopic technique of choice for deriving molecular-scale information on the attachment geometry of organic molecules at solid-water interfaces (Hind et al ., 2001) as demonstrated by Per Persson (Umeå University) and co-workers (e.g., Axe et al ., 2006;Boily et al ., 2000) . In a series of in situ ATR-FTIR studies, we examined the interaction of (1) oxalate (C 2 O 4 2-) with a-Al 2 O 3 (corundum) and g-AlOOH (boehmite) Johnson et al ., 2004b), (2) (Johnson et al ., 2005a)…”