Hong Phuc Vu

Thiocyanate adsorption on ferrihydrite and its fate during ferrihydrite transformation to hematite and goethite.

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.

Biodegradation of thiocyanate by a novel strain of Burkholderia phytofirmans from soil contaminated by gold mine tailings

A novel B. phytofirmans strain with the capacity to degrade thiocyanate was isolated from pH approximately 6·5 soil contaminated by effluent from gold mine tailings. This Burkholderia strain uses thiocyanate as its sole nitrogen source and can grow on acetate as a sole carbon source in a minimal medium. While biodegradation of thiocyanate has been reported to occur within alkaline environments (e.g. soda lakes and wastewater from coking plants), this work presents the first observation of thiocyanate degradation by Burkholderia at pH <9·0. Our findings therefore inform remediation strategies for thiocyanate contamination in nonalkaline soils and waters impacted by gold‐mining activities.

Transformation of ferrihydrite to hematite: an in situ investigation on the kinetics and mechanisms

Abstract The kinetics and mechanisms of the transformation of 2-line ferrihydrite (FH) to hematite (HM), in the presence of Pb at elevated temperatures and high pH condition, were elucidated using synchrotronbased, in situ energy dispersive X-ray diffraction (EDXRD). The time-resolved diffraction data indicated that HM crystallization occurred via a two-stage process. Based on the EDXRD data, combined with high-resolution electron microscopic images, an aqueous-aided 2D growth mechanism is proposed for both HM crystallization stages.