title: Arsenic incorporation in synthetic struvite (NH4MgPO4·6H2O): a synchrotron XAS and single-crystal EPR study.
abstract: Struvite, a common biomineral and increasingly important fertilizer recovered from wastewater treatment plants, is capable of sequestering a wide range of heavy metals and metalloids, including arsenic. Inductively coupled plasma mass spectrometric (ICPMS) analyses and microbeam synchrotron X-ray fluororescence (μ-SXRF) mapping show that struvite formed under ambient conditions contains up to 547 ± 15 ppm As and that the uptake of As is controlled by pH. Synchrotron As K-edge XANES spectra measured at 20 K show that As(5+) is the predominant oxidation state in struvite, irrespective of Na2HAsO4·7H2O or NaAsO2 as the source for As. Modeling of As K-edge EXAFS data suggest that local structural distortion associated with the substitution of As(5+) for P(5+) in struvite reaches up to 3.75 Å. Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated struvite disclose five [AsO3](2-) radicals and one [AsO4](2-) radical. These arsenic-centered oxyradicals are all readily attributed to form from diamagnetic [AsO4](3-) precursors during irradiation, providing further support for exclusive incorporation and local structural expansion beyond the first shell of As(5+) at the P site in struvite.
authors.affiliation: Department of Geological Sciences, University of Saskatchewan , Saskatoon, SK S7N 5E2, Canada.
authors.forename: Jinru
authors.initials: J
authors.lastname: Lin
authors.forename: Ning
authors.initials: N
authors.lastname: Chen
authors.forename: Yuanming
authors.initials: Y
authors.lastname: Pan
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D003460:Crystallization; D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D017616:Magnesium Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D000069877:Struvite; D013431:Sulfates / Q000737:chemistry; D017356:Synchrotrons; D056928:X-Ray Absorption Spectroscopy
chemical_list: D017616:Magnesium Compounds; D008903:Minerals; D010710:Phosphates; D013431:Sulfates; C543401:boussingaultite; D000069877:Struvite; D001151:Arsenic