Adsorption of Organic Matter at Mineral/Water Interfaces. 2. Outer-Sphere Adsorption of Maleate and Implications for Dissolution Processes

Abstract

The effects of the adsorption of a simple dicarboxylate low molecular weight organic anion, maleate, on the dissolution of a model aluminum oxide, corundum (alpha-Al2O3), have been examined over a range of different maleate concentrations (0.125-5.0 mM) and pH conditions (2-10). In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic measurements indicate that maleate binds predominantly as an outer-sphere, fully deprotonated complex ([triple bond]AlOH2+ -Mal2-) at the corundum surface over the entire range of maleate concentrations and pH conditions investigated. In accordance with the ATR-FTIR findings, macroscopic adsorption data can be modeled as a function of maleate concentration and pH using an extended constant capacitance approach and a single [triple bond]AlOH2+ -Mal2- species. Outer-sphere adsorption of maleate is found to significantly reduce the protolytic dissolution rate of corundum under acidic conditions (pH < 5). A likely mechanism involves steric protection of dissolution-active surface sites, whereby strong outer-sphere interactions with maleate hinder attack on those surface sites by dissolution-promoting species.

Modelling of the adsorption of phenolic acids onto α,γ–alumina particles

“…For the three ionic strengths, the optimized C values do not satisfy condition (9) (see Fig. 3), but they are of the same order of magnitude or lower than those used by other authors in low ionic strength conditions [35,[66][67][68][69]72]. As shown in Table 3, int K 1 , int K 2 and N s do not vary with ionic strength.…”

“…Due to the large linear part of the titration results, the fitting with DLM cannot converge. As some authors used this model at ionic strengths lower than 0.1 mol L −1 [35,[67][68][69], Lützenkirchen [50] stressed that some precautions must be taken so that this model makes sense under low ionic strength conditions. First, the relationship between the oxide charge (or sorbed H + ) and pH must be linear, which is verified in this work for our values of ionic strength, as shown in Fig.…”

“…For low surface coverage ([H 2 A] < 3 mmol L −1 ), the presence of acids favors dissolution, but for higher surface coverage the dissolution process is inhibited possibly because AlHA 2+ complex formed in solution can be sorbed onto the surface, but also because the ligand exchange on the surface is very rapid, as ligand concentration is very high and all ionizable surface sites are occupied, and do not permit the detachment of Al atom from the surface. Pyromellitic acid [13] (1,2,4,5-benzenetricarboxylic acid) and maleic acid [67] (Z-butenedioic acid) were shown to inhibit alumina dissolution when they are strongly associated with the alumina surface; these ligands can form multidentate complexes both the surface and with Al 3+ . It is worth noting that contrary to our work, the inhibition of dissolution was observed for all studied concentrations for pyromellitic [13] and maleic [67] acids.…”

“…Pyromellitic acid [13] (1,2,4,5-benzenetricarboxylic acid) and maleic acid [67] (Z-butenedioic acid) were shown to inhibit alumina dissolution when they are strongly associated with the alumina surface; these ligands can form multidentate complexes both the surface and with Al 3+ . It is worth noting that contrary to our work, the inhibition of dissolution was observed for all studied concentrations for pyromellitic [13] and maleic [67] acids.…”

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).…”