title: Kinetic Modeling of Phosphate Adsorption by Preformed and In situ formed Hydrous Ferric Oxides at Circumneutral pH.
abstract: Kinetics of phosphate removal by Fe(III) was investigated by both preformed and in situ formed hydrous ferric oxides (HFO) at pH 6.0-8.0. A pseudo-second-order empirical model was found to adequately describe phosphate removal in the two cases. The Elovich and intra-particle diffusion models, however, were only capable of describing phosphate adsorption to preformed HFO (PF-HFO). By using surface complexation kinetic models (SCKMs) to describe phosphate adsorption to PF-HFO, the adsorption rate constant (0.0386-0.205 mM-1min-1for SCKM-1 and 0.0680-0.274 mM-1min-1for SCKM-2) decreased with increasing pH while the protonation reaction rate constant in SCKM-2 (0.0776-0.0947 mM-1min-1) increased over the pH range 6.0-8.0. Using the rate constants obtained from the process of phosphate adsorption to PF-HFO, the amount of active surface sites on the in situ formed HFO were calculated as 0.955 ± 0.170, 1.46 ± 0.39 and 2.98 ± 0.78 mM for pH = 6.0, 7.0 and 8, respectively. Generally, as the SCKMs incorporate phosphate complexation on HFO surface sites and protons competiting for the surface sites, they could provide a good description of the rate and extent of phosphate removal by both preformed and in-situ formed HFO over a wide range of conditions.
authors.affiliation: National engineering laboratory for coal-fired pollutants emission reduction, School of Energy and Power Engineering, Shandong University, Jinan 250100, PR China.
authors.forename: Yanpeng
authors.initials: Y
authors.lastname: Mao
authors.affiliation: School of Environmental Science and Engineering, Shandong University, Jinan 250100, PR China.
authors.forename: Qinyan
authors.initials: Q
authors.lastname: Yue