Ni(II) complexation to amorphous hydrous ferric oxide: An X-ray absorption spectroscopy study

• Published in: Journal of colloid and interface science 2007-10, Vol.314 (1), p.10-17
• Main Authors: Xu, Ying, Axe, Lisa, Boonfueng, Thipnakarin, Tyson, Trevor A., Trivedi, Paras, Pandya, Kaumudi
• Format: Article
• Language: English
• Subjects: Absorption; Adsorption; Amorphous oxide; BIOLOGICAL AVAILABILITY; Chemistry; Colloidal state and disperse state; Exact sciences and technology; EXAFS; Ferric Compounds - chemistry; General and physical chemistry; GEOCHEMISTRY; GEOSCIENCES; Hydrous ferric oxide; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IRON HYDROXIDES; IRON OXIDES; national synchrotron light source; NICKEL; Nickel - chemistry; NICKEL COMPLEXES; NICKEL HYDROXIDES; SORPTION; Spectrum Analysis - methods; Surface physical chemistry; X-Ray Diffraction; X-Rays
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2007.05.037

Ni(II) sorption onto iron oxides and in particular hydrous ferric oxide (HFO) is among the important processes impacting its distribution, mobility, and bioavailability in environment. To develop mechanistic models for Ni, extended X-ray absorption fine structure (EXAFS) analysis has been conducted on Ni(II) sorbed to HFO. Coprecipitation revealed the formation of the metastable α-Ni(OH) 2 at a Ni(II) loading of 3.5 × 10 −3   mol g −1 . On the other hand, Ni(II) formed inner-sphere mononuclear bidentate complexes along edges of FeO 6 octahedra when sorbed to HFO surfaces with Ni–O distances of 2.05–2.07 Å and Ni–Fe distances of 3.07–3.11 Å. This surface complex was observed by EXAFS study over 2.8 × 10 −3 to 10 −1 ionic strength, pH from 6 to 7, a Ni(II) loading of 8 × 10 −4 to 8.1 × 10 −3   mol g −1 HFO, and reaction times from 4 hours to 8 months. The short- and long-range structure analyses suggest that the presence of Ni(II) inhibited transformation of the amorphous iron oxide into a more crystalline form. However, Ni 2+ was not observed to substitute for Fe 3+ in the oxide structure. This study systematically addresses Ni(II) adsorption mechanisms to amorphous iron oxide. The experimentally defined surface complexes can be used to constrain surface complexation modeling for improved prediction of metal distribution at the iron oxide/aqueous interface. Ni K-edge χ ( k ) × k 3 spectra of Ni–HFO sorption complexes as a function of pH, IS, adsorbate loading, and reaction time studied at room temperature.