title: Kinetics of phosphate adsorption on goethite: comparing batch adsorption and ATR-IR measurements.
abstract: The adsorption kinetics of phosphate on goethite has been studied by batch adsorption experiments and by in situ ATR-IR spectroscopy at different pH, initial phosphate concentrations and stirring rates. Batch adsorption results are very similar to those reported by several authors, and show a rather fast initial adsorption taking place in a few minutes followed by a slower process taking place in days or weeks. The adsorption kinetics could be also monitored by integrating the phosphate signals obtained in ATR-IR experiments, and a very good agreement between both techniques was found. At pH 4.5 two surface complexes, the bidentate nonprotonated (FeO)(2)PO(2) and the bidentate protonated (FeO)(2)(OH)PO complexes, are formed at the surface. There are small changes in the relative concentrations of these species as the reaction proceeds, and they seem to evolve in time rather independently. At pH 7.5 and 9 the dominating surface species is (FeO)(2)PO(2), which is accompanied by an extra unidentified species at low concentration. They also seem to evolve independently as the reaction proceeds. The results are consistent with a mechanism that involve a fast adsorption followed by a slow diffusion into pores, and are not consistent with surface precipitation of iron phosphate.
authors.affiliation: Departamento de Química, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahía Blanca, Argentina. cluengo@uns.edu.ar
authors.forename: Carina
authors.initials: C
authors.lastname: Luengo
authors.forename: Maximiliano
authors.initials: M
authors.lastname: Brigante
authors.forename: Juan
authors.initials: J
authors.lastname: Antelo
authors.forename: Marcelo
authors.initials: M
authors.lastname: Avena
mesh_terms: D000327:Adsorption; D002627:Chemistry, Physical / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals; D010087:Oxides / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D058085:Iron Compounds; D008903:Minerals; D010087:Oxides; D010710:Phosphates; D014867:Water; C094886:goethite; D007501:Iron