title: Phosphate bonding on noncrystalline Al/Fe-hydroxide coprecipitates.
abstract: Poorly crystalline minerals have high sorption capacities for environmentally important chemical species, but molecular-level mechanisms of sorption on complex mineral assemblages remain largely unknown. We determined the distribution of orthophosphate (PO(4)) bonding between Al and Fe in relation to structural properties of Al/Fe-hydroxide coprecipitates. Phosphate was sorbed at concentrations between 0.042 and 0.162 mol P mol(-1) Al+Fe on coprecipitates containing 0, 20, 50, 75, or 100 mol % of metal as Al. Phosphorus XANES analyses showed preferential bonding of PO(4) for Al on coprecipitates with 20 and 50 mol % Al, and no preference for either metal at 75 mol % Al, consistent with X-ray photoelectron spectroscopy (XPS) analyses of near-surface metal distributions. Structural ordering and the Fe-hydroxide domain size in coprecipitates decreased with increasing Al proportion, as shown by X-ray diffraction (XRD) and Fe EXAFS analyses. Structural interactions in coprecipitates imparted unique PO(4) sorption properties compared with isolated Al- or Fe-hydroxide.
authors.affiliation: Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27695, United States.
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Liu
authors.forename: Dean
authors.initials: D
authors.lastname: Hesterberg
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D011232:Chemical Precipitation; D003460:Crystallization; D006878:Hydroxides / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D010710:Phosphates / Q000737:chemistry*; D010758:Phosphorus / Q000032:analysis; D013696:Temperature; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D006878:Hydroxides; D010710:Phosphates; D010758:Phosphorus; D000535:Aluminum; D007501:Iron