title: Coprecipitated arsenate inhibits thermal transformation of 2-line ferrihydrite: implications for long-term stability of ferrihydrite.
abstract: 2-line ferrihydrite, a ubiquitous iron oxy-hydroxide found in natural and engineered systems, is an efficient sink for the toxic metalloids such as arsenic. While much is known of the excellent capacity of ferrihydrite to coprecipitate arsenate, there is little information concerning the long-term stability of arsenate-accumulated ferrihydrite. By thermal treatment methodology, the expedited transformation of ferrihydrite in the presence of coprecipitated arsenate was studied at varying As/Fe ratios (0-0.5) and different heating temperature (40, 300, 450, 600°C). Pure and transformed minerals were characterized by thermogravimetry (TG), X-ray diffraction (XRD), Electron Spin Resonance (ESR), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Fourier Transform Infrared Spectroscopy (FTIR). Arsenate was found to retard the thermal transformation of ferrihydrite. The extents of ferrihydrite transformation to hematite decreased with increasing As/Fe ratios, but increased at a higher heating temperature. It is predicted that the coprecipitated arsenate can stabilize the amorphous iron oxides against the transformation to more crystalline solids. Arsenate concentration appears to play an important role in this predicted long-term stability.
authors.affiliation: Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia; College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China. Electronic address: zhaohui.wang@scu.edu.au.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
authors.forename: Dongxue
authors.initials: D
authors.lastname: Xiao
authors.affiliation: Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Bush
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D011232:Chemical Precipitation; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D001149:Arsenates; D005290:Ferric Compounds; C000499:ferric oxide; C092844:ferric oxyhydroxide
keywords: 2-line ferrihydrite; Arsenic; Co-precipitation; Electron spin resonance; Hematite