Characterization of Soil Clay Minerals Using Mid-infrared Spectroscopy

Clay mineral is one of the most important components in soil, and the characterization of soil clay is very useful to study the interactions between soil clay and soil organic materials. Chemical analysis of soil clay is time-consuming, while the infrared spectroscopic method seems promising. In this research, the characterization of three source clay minerals, i.e. illite, kaolin and montmorillonite, were analyzed using three mid-infrared spectroscopic techniques (attenuated total reflectance (FTIR-ATR), transmittance spectroscopy, and photoacoustic spectroscopy (FTIR-PAS)). For the FTIR transmittance spectra of the three source clays, there were three main absorption regions: 2600 similar to 3800 cm(-1),1300 similar to 1800 cm(-1), and 5001200 cm(-1), and sharp differences could be found in each region; for the FTIR-ATR spectra of the three source clays, there were absorptions with minor difference in the region of 800 similar to 4200 cm(-1); for the FTIR-PAS spectra of the three source clays, there were also three similar absorption regions as FTIR transmittance spectra, but more absorptions were found in the FTIR-PAS spectra comparing with FTIR transmittance absorptions. Comprehensively, FTIR-PAS spectroscopy showed more merits in the characterization of soil clays among the three infrared spectroscopic techniques. The FTIR-PAS was applied to charactrize three soil types, and the interactions between soil clay and soil organic materials could be studied using the step-scaning function of FTIR-PAS.