New Insight into the Local Structure of Hydrous Ferric Arsenate Using Full-Potential Multiple Scattering Analysis, Density Functional Theory Calculations, and Vibrational Spectroscopy

Shaofeng Wang (1) , Xu Ma (1) , Guoqing Zhang (1) , Yongfeng Jia (2) , Keisuke Hatada (3)

1 Institute of Applied Ecology
2 Institute of Environmental Protection
3 IPR - Institut de Physique de Rennes

Hydrous ferric arsenate (HFA) is an important arsenic-bearing precipitate in the mining-impacted environment and hydrometallurgical tailings. However, there is no agreement on its local atomic structure. The local structure of HFA was reprobed by employing a full-potential multiple scattering (FPMS) analysis, density functional theory (DFT) calculations, and vibrational spectroscopy. The FPMS simulations indicated that the coordination number of the As Fe, Fe As, or both in HFA was approximately two. The DFT calculations constructed a structure of HFA with the formula of Fe(HAsO4)(x)(H2AsO4)(1-x)(OH))(y)center dot zH(2)O. The presence of protonated arsenate in HFA was also evidenced by vibrational spectroscopy. The As and Fe K-edge X-ray absorption near-edge structure spectra of HFA were accurately reproduced by FPMS simulations using the chain structure, which was also a reasonable model for extended X-Ray absorption fine structure fitting. The FPMS refinements indicated that the interatomic Fe-Fe distance was approximately 5.2 angstrom, consistent with that obtained by Mikutta et al. (Environ. Sci. Technol. 2013, 47 (7), 3122-3131) using wavelet analysis. All of the results suggested that HFA was more likely to occur as a chain with AsO4, tetrahedra and FeO6 octahedra connecting alternately in an isolated bidentate-type fashion. This finding is of significance for understanding the fate of arsenic and the formation of ferric arsenate minerals in an acidic environment.

Keywords: fine-structure spectroscopy; ray-absorption spectroscopy; experimental xanes spectra; crystalline scorodite; atomic-structure; raman-spectroscopy; group aso3oh; precipitation; ferrihydrite; sulfate

Domains: Chemical Sciences; Theoretical and/or physical chemistry; Environmental Sciences; Environmental Engineering; Physics [physics]; Physics [physics]; Chemical Physics [physics.chem-ph]

Shaofeng Wang, Xu Ma, Guoqing Zhang, Yongfeng Jia, Keisuke Hatada. New Insight into the Local Structure of Hydrous Ferric Arsenate Using Full-Potential Multiple Scattering Analysis, Density Functional Theory Calculations, and Vibrational Spectroscopy. Environmental Science and Technology, 2016, 50 (22), pp.12114-12121. ⟨10.1021/acs.est.6b02703⟩. ⟨hal-01437439⟩