Qualitative and Quantitative Determination of Montmorillonite Using Infrared Spectrometry

Abstract

The present study investigates the various possibilities of qualitative and quantitative analysis of montmorillonite (1/2Ca, Na) 0.7 (Al, Mg, Fe) 4 (Si, Al) 8O20 (OH) 4. n H2O (MT), major constituent of Bendonite coming the island Milos-Greece, using infrared (IR) spectroscopy and preparing the samples with KBr. X-Ray diffraction diagrams were obtained for the determination of their mineralogical composition. Observation of IR spectra of sample with different MT content revealed that the Si-O-Si vibration band at 1038cm-1 sharpens with increasing MT content. The combination of the above techniques led to a convenient determination of the minerals, contained in the sample and to a discrimination of identical oscillations, observed in different minerals at the same wave number (1038cm-1)[1]. As far as the quantitative analysis concerns, in the case of MT, thirteen comparative samples of known composition were analysed. The obtained spectra were digitized and smoothed, within the area from 800 to 1200 cm-1, using the Savitzky – Golay method, followed by Lorentz function transformation. Due to overlap from other substances, the plot of a calibration curve for MT, and consequently the development of a model, describing the absorption / concentration correlation for a specific sample, were not satisfactory. So the calibration curve according to Lambert- Beer law [2, 3], required use of samples with high concentration of MT. To overcome this problem the calibration curve for MT was constructed using dilutions of standard samples containing more than 85% of the mineral, with SiO2, at the wave number of 1038cm-1. This curve was used for the determination of MT in unknown samples giving very good results compared with the mineralogical composition obtained by XRD.