title: Thiocyanate adsorption on ferrihydrite and its fate during ferrihydrite transformation to hematite and goethite.
abstract: Thiocyanate (SCN(-)) is a toxic contaminant produced by industrial processes such as gold ore cyanidation and coal coking. The potential for remediation by adsorption of SCN(-) on ferrihydrite, the influence of sulfate (SO4(2-)) on SCN(-) adsorption, and the fate of adsorbed SCN(-) during ferrihydrite aging were studied using macroscopic techniques complemented with attenuated total reflectance-Fourier transform infrared analysis (ATR-FTIR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Results showed that adsorption of SCN(-) was strongly affected by the concentration of electrolyte (NaNO3) and pH, with decreases in concentration of NaNO3 and pH leading to increased SCN(-) adsorption. The adsorption isotherms can be described by the Langmuir model. While at lower concentrations (0.52-1.04 mM), the presence of SO4(2-) had little impact on SCN(-) adsorption, at a higher concentration (2.08 mM), SCN(-) adsorption was significantly inhibited. ATR-FTIR data confirmed that SCN(-) was bound as an outer-sphere complex on ferrihydrite, and this mechanism was not influenced by changes in pH or electrolyte concentration. XRD data showed that ferrihydrite transformed to a mixture of hematite and goethite at 75 °C and pH 5 in the presence and absence of SCN(-). Partitioning data revealed that during ferrihydrite transformation, all adsorbed SCN(-) was released into solution.
authors.affiliation: School of Earth Sciences, University of Melbourne, Victoria 3010, Australia. Electronic address: hong.vu@unimelb.edu.au.
authors.forename: Hong Phuc
authors.initials: HP
authors.lastname: Vu
authors.affiliation: School of Earth Sciences, University of Melbourne, Victoria 3010, Australia.
authors.forename: John W
authors.initials: JW
authors.lastname: Moreau
mesh_terms: D000327:Adsorption; D004785:Environmental Pollutants / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000737:chemistry; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013431:Sulfates / Q000737:chemistry; D013861:Thiocyanates / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D004785:Environmental Pollutants; D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D009566:Nitrates; D013431:Sulfates; D013861:Thiocyanates; C094886:goethite; C000499:ferric oxide; C092844:ferric oxyhydroxide; C031618:sodium nitrate; C031760:thiocyanate
keywords: Adsorption; Fate; Ferrihydrite; Iron oxides; Remediation; Thiocyanate