The large amount of water in the interlamellar space of alkylammonium montmorillonites in aqueous solutions is not fixed by intercalated hexanol or octanol. The hydration of the NH3+-group and the filling of the empty spaces between the carbon chains are responsible for this phenomenon. Hydrogen bonds between the alcohols and the ammonium groups reduce the enthalpy of solution of hexanol and octanol in the interlamellar region at infinite dilution to +17.6 and +12.7 kJ/mole, respectively. Self-association of the alcohols further diminishes the enthalpy of solution at higher alcohol concentration. The interlamellar fixation of the RNH3 cations prevents a micellization as has been obtained in bulk solutions. At a given alcohol concentration smectic type aggregates, i.e., double layers of alcohol molecules, appear as shown by an increase of the basal spacing of the organo-clay complexes. The aggregate formation is favored by a longer chain length of both the cation and the alcohol.

Two clay fractions of a Cambrian claystone from Estonia, consisting essentially of illite and 20% expandable illite-smectite, (I-S) were treated with C12 and C18 alkylammonium cations for K-exchange. Both the untreated and treated samples were dated by the K-Ar method. The treated clays lost several percent of their original K2O, with greater losses for longer-chain cations and for longer reaction time, in accordance with previously published studies. The dates of the treated clay fractions were 20–30 Ma lower than those of the untreated clays. The decrease in the dates suggests preferential opening of older, detrital clays. The K-Ar dates of the illite layers susceptible to K extraction by the various treatments were calculated by subtracting K2O and radiogenic 40Ar values of the consecutive step products, and they were plotted against the total % K2O removed, used as an indicator of the reaction progress. Extrapolation of the plot revealed a detrital (1550 Ma) and a diagenetic (380 Ma) age for the 2 illitic minerals present in the investigated shale sample. The inferred Devonian age of diagenesis of the Estonian clay corresponds to the period of massive dolomitization in the area. Both alteration processes can be related to a Devonian incursion of hot or alkaline fluids, which helps to explain the occurrence of 20% expandable I-S in claystones that have never been buried more than 1000 m.

Extrapolated K-Ar ages and K2O contents of the illitic minerals, estimated from the X-ray diffraction (XRD) data, were used to model the experimental data. A good agreement was reached when dilution effects (chlorite and expanded illite) were taken into account.

The potential use of near-infrared (NIR) spectroscopy as a characterization tool for organo-clays would be a great asset but little work has been done in this regard because the application of NIR to clay mineral studies is a relatively new phenomenon. The purpose of this study was to use NIR spectroscopy to investigate the effect of alkylammonium cations on the acid dissolution of a high-charge montmorillonite (SAz-1). Detailed analysis of the spectra of Li+-, TMA+- (tetramethylammonium), and HDTMA+- (hexadecyltrimethylammonium) saturated SAz-1 montmorillonite in the NIR region was achieved by comparing the first overtone (2ν) and combination (ν+δ) bands of XH groups (X = O, C) with the fundamental stretching (ν) and bending (δ) vibrations observed in the mid-infrared (MIR) region. Comprehensive analysis of the vibrational modes of CH3-N, CH3-C, and -CH2-C groups of TMA+ and HDTMA+ cations detected in the MIR and NIR regions was also performed. Both MIR and NIR spectra demonstrated that exchange of Li+ by TMA+ only slightly improved the resistance of SAz-1 layers to dissolution in 6 M HCl at 80°C, while exchange by the larger HDTMA+ cations almost completely protected the montmorillonite layers from acid attack. Use of NIR spectra in reaching these conclusions was crucial. Only in the NIR region could the creation of SiOH groups be monitored, which is an important indicator of the acidification of the montmorillonite surface. The OH-overtone region in the spectra of Li-SAz-1 and TMA-SAz-1 revealed that the SiOH band near 7315 cm−1 increases in intensity with enhanced acid treatment. In contrast, no SiOH groups were identified in the NIR spectra of HDTMA-SAz-1 treated in HCl, indicating that HDTMA+ completely covers the inner and outer surfaces of the montmorillonite and hinders access ofprotons to the Si-O− bonds created upon acid treatment.

Sorption of the polar insecticide imidacloprid on organic-saturated octadecylammonium (C18) and dioctadecyldimethylammonium (DOD) and inorganic- (Fe- ) saturated Wyoming (W) and Arizona (A) montmorillonites has been investigated. Sorption isotherms were fitted to the Freundlich equation. Imidacloprid-montmorillonite complexes were studied by X-ray diffraction and FT-IR techniques. Imidacloprid sorption coefficients, Kf, decreased in the order WC18> AC18> WFe> WDOD≥ ADOD. The low layer charge and saturation by primary alkylammonium cation facilitates sorption of imidacloprid in the interlayer of the smectite, corroborated by the increase in basal spacing observed in X-ray diffraction patterns and by the presence of absorption band shifts in FT-IR spectra. Imidacloprid sorbs in the interlayer space of smectite mainly by hydrophobic interactions with the alkyl chains in organic smectites and with the uncharged siloxane surface in Fe(III)-smectite. Further polar bonds between the NO2 group of imidacloprid and the NH of the primary alkyl cations and protonation of imidacloprid in Fe-smectites enhanced sorption in these cases.