Application of Raman spectroscopy to identify iron minerals commonly found in mine wastes

Raman spectroscopy can be used for the rapid identification of a wide variety of minerals ranging from common iron oxy(hydroxides), such as ferrihydrite, to rare minerals, such as adelite. This study employed Raman spectroscopy (laser power 0.1%) to characterize both synthetic and common natural iron-bearing mineral phases, including oxides (hematite, magnetite), hydroxides (ferrihydrite, goethite, lepidocrocite, akaganéite), carbonate (siderite), sulfate (Na-jarosite), and ferric arsenates (scorodite, yukonite), found in acid mine drainage and mine tailings settings. X-ray diffraction (XRD) was conducted to verify the purity of phases and compared with associated Raman analyses. Samples with arsenate adsorbed onto ferrihydrite at varied As/Fe ratios (0.50, 0.10, and 0.05) at pH ~ 10 were also evaluated. Raman spectra were compared with the literature and recommendations made regarding Raman bands that are the most diagnostic for the individual iron minerals studied. Comparison of the Raman and XRD scans shows Raman can either augment or replace XRD for mineral identification. Lastly, some important applications of Raman spectrometry for evaluating significant environmental processes are discussed.