US EPA

2088500 

Journal Article 

Arsenic incorporation in synthetic struvite (NH4MgPO4•6H2O): A synchrotron XAS and single-crystal EPR study 

Lin, J; Chen, N; Pan, Y 

2013 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

47 

22 

12728-12735 

English 

24152131 

10.1021/es402710y 

WOS:000327360600016 

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 flurorescence (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 As5+ 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 As5+ for P5+ 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 As5+ at the P site in struvite.