In situ FTIR study on the dehydration of natural goethite

Fourier Transform Infrared (FTIR) spectroscopy, thermal analysis -Differential Scanning Calorimetry (DSC) and Thermo-Gravimetry (TG-DTG) were used to study the dehydration behavior of synthetic goethite and two naturally occurring goethite samples (Natural I and Natural 2) from Banded Iron Formation (BIF), at C.S. Halli, Chitradurg district, Karnataka, India. Goethites and its dehydration products were also identified by powder X-ray Diffraction (XRD) method. The dehydration temperatures were at 538, 567 and 578 K for synthetic, Natural 1 and 2 goethite, respectively. On approaching the dehydration temperature, infrared active modes of the hydroxyl groups have shown distinct variations. The peak position for the stretching mode around 3150 cm(-1) was shifted upwards, while that for in-plane-deformation mode around 890 cm(-1) was down shifted indicating weakening of strength of the hydrogen bonding. No intermediate phase, so called hydro-hematite, was observed in these studies. The total absorbance (area under the peak) of these modes have shown the Arrehenius type behavior in the temperature range 500-600 K, using which the activation energy for the dehydration process was estimated as 71, 103 and 85 kJ/mol for synthetic, Natural 1 and 2 goethites respectively. (c) 2005 Elsevier Ltd. All rights reserved.