Simultaneous inner-and outer-sphere arsenate adsorption on corundum and hematite.

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Geochim. Cosmochim. Acta

DOI:https://doi.org/10.1016/j.gca.2008.02.013· OSTI ID:929272

Catalano, J G; Park, C; Fenter, P; Zhang, Z

The ability to predict the fate and transport of arsenic in aquatic environments, its impact on water quality and human health, and the performance and cost-effectiveness of water treatment systems relies on understanding how it interacts with solid surfaces. In situ resonant surface X-ray scattering measurements of arsenate adsorption at pH 5 in 0.01 M NaCl on corundum and hematite (012) surfaces demonstrate that arsenate surface complexation is unexpectedly bimodal, adsorbing simultaneously as inner- and outer-sphere species. In addition, this bimodal behavior is found to be independent of the total arsenate solution concentration, and thus surface coverage, over the range of 10{sup -6} to 10{sup -3} M. Alternative mechanisms to produce the observed As distributions, such as arsenate dimerization or surface precipitation of an aluminum or ferric arsenate, are inconsistent with the experimentally-determined total and As-specific density profiles. Based on the location of the outer-sphere arsenate in relation to the surfaces studied, possible binding mechanisms include electrostatic attraction, hydrogen bonding to surface oxygen functional group, and configurational stabilization by interfacial water. Although the observation of outer-sphere arsenate surface complexes on a metal oxide surface is unprecedented, it is unclear if such species were absent in previous molecular-scale studies, as it is difficult for methods commonly used to investigate the mechanisms of arsenate adsorption to conclusively identify or rule out the presence of outer-sphere species when inner-sphere species are also present.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 929272
• Report Number(s): ANL/XSD/JA-61799
• Journal Information: Geochim. Cosmochim. Acta, Journal Name: Geochim. Cosmochim. Acta Journal Issue: 8 ; 2008 Vol. 72; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

08 HYDROGEN
ADSORPTION
ALUMINIUM
ARSENATES
ARSENIC
BONDING
CORUNDUM
DIMERIZATION
ELECTROSTATICS
FUNCTIONALS
HEMATITE
HYDROGEN
OXIDES
OXYGEN
PRECIPITATION
SCATTERING
STABILIZATION
WATER QUALITY
WATER TREATMENT