Kinetics of sulfate and selenate adsorption/desorption onto γ-Al2O3 by the pressure-jump technique
Journal
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering
Journal Volume
34
Journal Issue
3
Pages
605-624
Date Issued
1999
Author(s)
Abstract
Sulfate and selenate adsorption/desorption on γ-Al2O3 in aqueous suspension were investigated thermodynamically and kinetically. The triple- layer model fit the experimental data well when adsorbed sulfate and selenate were assumed to form outer-sphere complexes (SOH2+-SO42- and SOH2+- SeO42-). The intrinsic equilibrium constants (K(eq)(int)) of the complex were 1010.9 M-2 for SOH2+-SO42- and 1010.6 M-2 for SOH2+- SeO42-. Pressure-jump relaxation was used to determine the kinetics of SO42- and SeO42- adsorption/desorption on γ-Al2O3. A single relaxation was observed due to the adsorption/desorption processes. Based on the relaxation theory and combined results of TLM simulations, a single-step process is proposed. The intrinsic values of the adsorption and desorption rate constants were determined to be k1(int) = 2.7 x 108 M-2s-1 and k- 1(int) = 1.I x 10-2 s-1 in the SO42-/γ-Al2O3 system and k1(int) = 4.3 x 108 M-2s-1 and k-1(int) = 4.4 x 10-2 s-1 in the SO42- /γ-Al2O3 system. The intrinsic equilibrium constants from kinetic measurements (K(kin)(int)) were 1010.4 M-2 for SO42- and 1010 M- 2 for SeO42-, which were similar to the intrinsic equilibrium constants (K(eq)(int)) 1010.9 M-2 for SO42- and 1010.6 M-2 for SeO42- , from the equilibrium studies. Sulfate and selenate adsorption/desorption on γ-Al2O3 in aqueous suspension were investigated thermodynamically and kinetically. The triple-layer model fit the experimental data well when adsorbed sulfate and selenate were assumed to form outer-sphere complexes (SOH2+-SO42- and SOH2+-SeO42-). The intrinsic equilibrium constants (Keqint) of the complex were 1010.9 M-2 for SOH2+-SO42- and 1010.6 M-2 for SOH2+-SeO42-. Pressure-jump relaxation was used to determine the kinetics of SO42- and SeO42- adsorption/desorption on γ-Al2O3. A single relaxation was observed due to the adsorption/desorption processes. Based on the relaxation theory and combined results of TLM simulations, a single-step process is proposed. The intrinsic values of the adsorption and desorption rate constants were determined to be k1int = 2.7×108 M-2s-1 and k-1int = 1.1×10-2 s-1 in the SO42-/γ-Al2O3 system and k1int = 4.3×108 M-2s-1 and k-1int = 4.4×10-2 s-1 in the SO42-/γ-Al2O3 system. The intrinsic equilibrium constants from kinetic measurements (Kkinint) were 1010.4 M-2 for SO42- and 1010 M-2 for SeO42-, which were similar to the intrinsic equilibrium constants (Keqint) 1010.9 M-2 for SO42- and 1010.6 M-2 for SeO42-, from the equilibrium studies.
SDGs
Type
journal article