Investigations into the kinetics and thermodynamics of Sb(III) adsorption on goethite (α-FeOOH)

Summary, in English

This study reports thermodynamic and kinetic data of Sb(III) adsorption from single metal solutions onto synthetic aqueous goethite (α-FeOOH). Batch equilibrium sorption experiments were carried out at 25 °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 ≥ 0.891) and Freundlich (R² ≥ 0.990) isotherms and the following parameters were derived from triplicate experiments: K_f = 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 Q_max = 61 ± 8 mg / g for the Langmuir model. The thermodynamic parameters determined were the equilibrium constant, K_eq = 1.323 ± 0.045, and the Gibb's free energy, Δ G⁰ = - 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.

• Author: Rhyadd Watkins; Dominik Weiss; William Dubbin; Kate Peel; Barry Coles; Tim Arnold
• Publishing year: 2006-11-15
• Language: English
• Pages: 639-646
• Publication/Series: Journal of Colloid and Interface Science
• Volume: 303
• Issue: 2
• Links: http://dx.doi.org/10.1016/j.jcis.2006.08.044
• Document type: Journal article
• Publisher: Academic Press
• Keywords: Adsorption; Goethite; Isotherms; Kinetics; Sb(III); Sb(V); Speciation; Thermodynamics
• Status: Published
• ISBN/ISSN/Other: ISSN: 0021-9797