An infrared spectroscopic study of the interaction of nontronite and ferruginous montmorillonites with alkali metal hydroxides

Abstract

AbstractIR spectroscopy has been used to study the interaction of alkali metal hydroxides with dioctahedral smectites having iron contents of 0·7% (montmorillonite) to 22% (nontronite), in connection with the alkali-stabilization of soils. The results have shown that the alkalis (LiOH, NaOH, KOH and CsOH) deprotonate hydroxyl groups co-ordinated to octahedral ferric iron, causing distortion of tetrahedral and octahedral layers. This concept of distortion is supported by a striking change in Mössbauer spectra and a large increase in b cell dimensions. The perturbation of the smectite structure, shown by shifts in the Si-O and O-H stretching vibrations, is greater for Na, K and Cs than for Li, suggesting that the larger cations interact with surface oxygens around the hexagonal hole. IR spectra suggest that the effect of NaOH on nontronite is substantially reversed by treating the smectite with CO2 or acetic acid vapour or by washing it with dilute salt solution, although Mössbauer spectroscopy and XRD indicate that the structure of the regenerated smectite is more disordered than that of the original.