title: XANES investigation of phosphate sorption in single and binary systems of iron and aluminum oxide minerals.
abstract: Phosphate sorption on Fe- and Al-oxide minerals helps regulate the solubility and mobility of P in the environment. The objective of this study was to characterize phosphate adsorption and precipitation in single and binary systems of Fe- and Al-oxide minerals. Varying concentrations of phosphate were reacted for 42 h in aqueous suspensions containing goethite, ferrihydrite, boehmite, or noncrystalline (non-xl) Al-hydroxide, and in 1:1 (by mass) mixed-mineral suspensions of goethite/boehmite and ferrihydrite/ non-xl Al-hydroxide at pH 6 and 22 degrees C. X-ray absorption near edge structure (XANES) spectroscopy was used to detect precipitated phosphate and distinguish PO4 associated with Fe(III) versus Al(III) in mixed-mineral systems. Changes in the full width at half-maximum height (fwhm) in the white-line peak in P K-XANES spectra provided evidence for precipitation in Al-oxide single-mineral systems, but not in goethite or ferrihydrite systems. Similarly, adsorption isotherms and XANES data showed evidence for precipitation in goethite/boehmite mixtures, suggesting that mineral interactive effects on PO4 sorption were minimal. However, sorption in ferrihydrite/non-xl Al-hydroxide systems and a lack of XANES evidence for precipitation indicated that mineral interactions inhibited precipitation in these binary mixtures.
authors.affiliation: Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27695-7619, USA.
authors.forename: Nidhi
authors.initials: N
authors.lastname: Khare
authors.forename: Dean
authors.initials: D
authors.lastname: Hesterberg
authors.forename: James D
authors.initials: JD
authors.lastname: Martin
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D011232:Chemical Precipitation; D005290:Ferric Compounds; D005293:Ferritins / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals; D010710:Phosphates / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D010710:Phosphates; C094886:goethite; C092844:ferric oxyhydroxide; D005293:Ferritins; D000537:Aluminum Oxide