title: Investigations into the kinetics and thermodynamics of Sb(III) adsorption on goethite (alpha-FeOOH).
abstract: This study reports thermodynamic and kinetic data of Sb(III) adsorption from single metal solutions onto synthetic aqueous goethite (alpha-FeOOH). Batch equilibrium sorption experiments were carried out at 25 degrees C over a Sb:Fe molar range of 0.005-0.05 and using a goethite concentration of 0.44 g Fe/L. Experimental data were successfully modelled using Langmuir (R2 > or = 0.891) and Freundlich (R2 > or = 0.990) isotherms and the following parameters were derived from triplicate experiments: Kf = 1.903 +/- 0.030 mg/g and 1/n = 0.728 +/- 0.019 for the Freundlich model and b = 0.021 +/- 0.003 L/mg and Qmax = 61 +/- 8 mg/g for the Langmuir model. The thermodynamic parameters determined were the equilibrium constant, Keq =1.323 +/- 0.045, and the Gibb's free energy, DeltaG0 = -0.692 +/- 0.083 kJ/mol. The sorption process is very fast. At a Sb:Fe molar ratio of 0.05, 40-50% of the added Sb is adsorbed within 15 min and a steady state is achieved. The experimental data also suggest that desorption can occur within 24 h of reaction due to the oxidation of Sb(III) on the goethite surface. Finally, calculated pH of the aqueous solution using MINTEQ2 agrees well with the measured pH (3.9 +/- 0.7; n = 30). At pH 4, the dominant Sb species in solution are Sb(OH)3 and HSbO2 which both likely adsorb as inner sphere complexes to the positively charged goethite surface.
authors.affiliation: Department of Earth Science Engineering, Imperial College London, South Kensington, London, SW7 2AZ, United Kingdom.
authors.forename: Rhyadd
authors.initials: R
authors.lastname: Watkins
authors.forename: Dominik
authors.initials: D
authors.lastname: Weiss
authors.forename: William
authors.initials: W
authors.lastname: Dubbin
authors.forename: Kate
authors.initials: K
authors.lastname: Peel
authors.forename: Barry
authors.initials: B
authors.lastname: Coles
authors.forename: Tim
authors.initials: T
authors.lastname: Arnold
mesh_terms: D000327:Adsorption; D000965:Antimony / Q000737:chemistry*; D003198:Computer Simulation; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals; D015394:Molecular Structure; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D058085:Iron Compounds; D008903:Minerals; D014867:Water; C094886:goethite; D000965:Antimony