title: Adsorption kinetics, capacity and mechanism of arsenate and phosphate on a bifunctional TiO2-Fe2O3 bi-composite.
abstract: Mixed oxide TiO(2)-Fe(2)O(3) bi-composites have been recognised as efficient and economical sorbents with great promise for arsenic removal from groundwater. In this study, we use a fast, simple and inexpensive synthesis method for this type of bi-composite and assess its adsorption performance. The kinetics of arsenate and phosphate adsorption onto the bi-composite are determined, demonstrating rapid and stable uptake of both oxy-anions over several days and with improved performance compared to the widely used TiO(2) sorbent. A modified pseudo-second order rate equation is introduced, which allows the adsorption kinetics to be modelled as two simultaneous, parallel reaction pathways with separate kinetic parameters. This equation reproduces the experimental observations accurately across a wide range of timescales from minutes to days. Our experimental data agrees with previous interpretations of the adsorption mechanism including the formation of mono-dentate and bi-dentate inner-sphere surface complexes. The arsenate and phosphate uptake capacities of the bi-composite are reported. Equilibrium studies were conducted between pH 5 and 9 and interpreted within the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models.
authors: Department of Earth Science & Engineering, Imperial College London, London SW7 5PD, United Kingdom. mitchall.darcy06@imperial.ac.uk
authors: Mitch
authors: M
authors: D'Arcy
authors: Dominik
authors: D
authors: Weiss
authors: Michael
authors: M
authors: Bluck
authors: Ramon
authors: R
authors: Vilar
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D010316:Particle Size; D010710:Phosphates / Q000737:chemistry*; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D001149:Arsenates; D005290:Ferric Compounds; D010710:Phosphates; C009495:titanium dioxide; C000499:ferric oxide; D014025:Titanium; C025657:arsenic acid