title: In situ imaging of interfacial precipitation of phosphate on Goethite.
abstract: Adsorption and subsequent immobilization of orthophosphate on iron oxides is of considerable importance in soil fertility and eutrophication studies. Here, in situ atomic force microscopy (AFM) has been used to probe the interaction of phosphate-bearing solutions with goethite, α-FeOOH, (010) cleavage surfaces. During the dissolution of goethite we observed simultaneous nucleation of nanoparticles (1.0-3.0 nm in height) of iron phosphate (Fe-P) phases at the earliest nucleation stages, subsequent aggregation to form secondary particles (about 6.0 nm in height) and layered precipitates under various pH values and ionic strengths relevant to acid soil solution conditions. The heterogeneous nucleation rates of Fe-P precipitates at phosphate concentrations ranging from 5.0 to 50.0 mM were quantitatively defined. Enhanced goethite dissolution in the presence of high concentration NaCl or AlCl3 leads to a rapid increase in Fe-P nucleation rates, whereas low concentration MgCl2 inhibits goethite dissolution, this in turn influences Fe-P nucleation. Moreover, kinetic data analyses show that low concentrations of citrate caused an increase in the nucleation rate of Fe-P phases. However, at higher concentrations of citrate, nucleation acceleration was reversed with much longer induction times to form Fe-P nuclei. These in situ observations may improve the mechanistic understanding of processes resulting in phosphate immobilization by goethite-rich acid soils in the presence of various inorganic and organic additive molecules.
authors.affiliation: †College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Wang
authors.affiliation: ‡Institut für Mineralogie, University of Münster, 48149 Münster, Germany.|§Department of Chemistry, Curtin University, P.O. Box U1987, Perth, Washington 6845, Australia.
authors.forename: Christine V
authors.initials: CV
authors.lastname: Putnis
authors.affiliation: ∥Department of Mineralogy and Petrology, University of Granada, Granada 18071, Spain.
authors.forename: Encarnación
authors.initials: E
authors.lastname: Ruiz-Agudo
authors.affiliation: ‡Institut für Mineralogie, University of Münster, 48149 Münster, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Hövelmann
authors.affiliation: ‡Institut für Mineralogie, University of Münster, 48149 Münster, Germany.|⊥The Institute for Geoscience Research (TIGeR), Curtin University, Perth, Washington 6102, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Putnis
mesh_terms: D000327:Adsorption; D011232:Chemical Precipitation; D002951:Citrates / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D018625:Microscopy, Atomic Force; D008903:Minerals / Q000737:chemistry*; D008956:Models, Chemical; D009994:Osmolar Concentration; D010710:Phosphates / Q000032:analysis* / Q000737:chemistry; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D012996:Solutions; D013499:Surface Properties
chemical_list: D002951:Citrates; D058085:Iron Compounds; D008903:Minerals; D010710:Phosphates; D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; C094886:goethite