Investigation of soils by thermal and spectroscopic analysis

Abstract

The present study assesses the potential usefulness of Fourier transform infrared spectroscopy (FTIR) spectroscopy and thermal analytical techniques to elucidate the mineralogical and organic matter (OM) framework of soils from Anaimalai situated in Coimbatore district, Tamil Nadu, India. Soil samples were procured from forests (AF1–AF3), agricultural land (AA1–AA3), and road side areas (AR1–AR3) along Anaimalai–Valparai region by random sampling method. FTIR spectra revealed the presence of silicates (quartz, orthoclase and microcline feldspars, kaolinite clay minerals), carbonates, and OM (organic carbon and humus) in the soils. The values of crystallinity index determined from FTIR were larger than one for all soils indicating that minerals in soils are highly disordered, with agricultural soils exhibiting slightly high disorderedness. From prior literature studies, it is known that only few seminal studies have highlighted the importance of application of thermal analytical techniques to soils. The present work demonstrates the feasibility of usage of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), in identifying the minerals smectite, calcite, and dolomite that could not be identified by FTIR spectroscopy. Specific heat capacities (Cp) of soils were determined from DSC and it can be inferred from the results that forest soils contain higher moisture content which in turn is indicative of good water retention for a healthy forest. Thus, the feasibility of various analytical techniques for soil analysis has been demonstrated.