XANES Investigation of Phosphate Sorption in Single and Binary Systems of Iron and Aluminum Oxide Minerals

摘要

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 noncrystatline(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 deg C.X-ray absorption near edge structure(XANES)spectroscopy was used to detect precipitated phosphate and distinguish PO_4 associated with Fe(lll)versus Al(lll)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 PO_4 sorption were minimal.However,sorption in ferrihydriteon-xl Al-hydroxide systems and a lack of XANES evidence for precipitation indicated that mineral interactions inhibited precipitation in these binary mixtures.