title: Surface complexation of antimony on kaolinite.
abstract: Geochemical fate of antimony (Sb) - a similar oxyanion as arsenic (As) - in a variety of environment is largely unexplored. Kaolinite is an important, naturally occurring clay mineral in soils and aquifers and is known to control the fate of several contaminants via a multitude of geochemical processes, primarily adsorption. Here we report adsorption of antimony on kaolinite as a function of solution chemistry: initial antimony concentration, pH, ionic strength, and a competing anion. A surface complexation modeling (SCM) approach was undertaken to understand the potential mechanistic implications of sorption envelope data. In the SCM, a multicomponent additive approach, in which kaolinite is assumed to be a (1:1) mixture of quartz (≡SiOH) and gibbsite (≡AlOH), was tested. Results indicated that ionic strength has a minimal effect on antimony adsorption. For the lower initial antimony concentration (4.11 μM), the additive model with binuclear surface complexes on quartz and gibbsite showed a better fit at pH<6, but somewhat under predicted the experimental data above pH 6. At the higher initial antimony concentration (41.1 μM), the sorption envelope was of different shape than the lower load. The additive model, which considered binuclear surface complexes for quartz and gibbsite, resulted in over prediction of the adsorption data at pH>3.5. However, the additive model with binuclear surface complex on quartz and mononuclear surface complex on gibbsite showed an excellent fit of the data. Phosphate greatly influenced antimony adsorption on kaolinite at both low and high antimony loadings, indicating competition for available surface sites.
authors.affiliation: Department of Agricultural and Environmental Sciences, Tennessee State University, 3500 John A. Merritt Blvd., Nashville, TN 37209-1561, USA. Electronic address: srakshit@tnstate.edu.
authors.forename: Sudipta
authors.initials: S
authors.lastname: Rakshit
authors.affiliation: Earth and Environmental Studies Department, Montclair State University, Montclair, NJ, USA.
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Sarkar
authors.affiliation: Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA.
authors.forename: Rupali
authors.initials: R
authors.lastname: Datta
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry*; D000965:Antimony / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D008956:Models, Chemical; D009994:Osmolar Concentration; D011791:Quartz / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011791:Quartz; D007616:Kaolin; D000536:Aluminum Hydroxide; D000965:Antimony
keywords: Antimony; Kaolinite; Sorption; Sorption-edge; Surface complexes