The highest frequency near-infrared (NIR) combination bands for specimens of four species of mica—montmorillonite-beidellite, illite, chlorite, and kaolinite—were correlated with respect to Al2O3 content. A direct linear correlation was found between the combination band positions and the Al2O3 contents of the montmorillonite-beidellite series, which may be given as: ν̄ cm−1 = (5.38 ± 0.04) (% Al2O3) + (4412.8 ± 0.9). A similar linear correlation for muscovite is: ν̄ cm−1 = (6.10 ± 0.25) (% Al2O3) + (4434.1 ± 8.3).

Possible NIR band interferences are shown for different mineral mixtures, along with the correlation of different illites with muscovite. No combination bands were found in the frequency region 4425 cm−1 to 4625 cm−1 for specimens in which the Al2O3 content was only in the tetrahedral layer sites.

Mechanically-prepared binary mixtures of two dioctahedral smectites (of different chemical compositions) with two kaolinites (with different amounts of structural defects) were studied by infrared (IR) spectroscopy to verify the ability of IR spectroscopy to detect small amounts of individual components in the mixtures. The same samples were analysed by X-ray diffraction (XRD) in transmission and reflection geometries to compare the sensitivities of these techniques. Infrared spectroscopy is suitable for detecting small amounts of kaolinite in the smectite-rich samples but is not sensitive to small amounts of smectite in kaolinite-rich samples. The IR spectra of kaolinite/ smectite mixtures have a ‘strongly kaolinitic character’ even with only 30% kaolinite. The most characteristic band of kaolinite, near 3695 cm–1, gradually decreased in intensity with decreasing kaolinite content though the presence of this absorption allowed 0.5 mass % of both kaolinites to be detected in their mixtures with smectites. On the other hand, XRD powder techniques are much more adept at detecting low smectite contents in kaolinite-rich samples.

Dioctahedral smectites (Cheto- and Wyoming-type montmorillonites and a beidellite) were treated with two hydrolysed OH-Al solutions (0.02 M in Al) containing different OH-Al complexes. The ratio of ∼3.25 mmol of Al per gram of smectite was used. The total Al and the presence of OH-Al species in solution before and after reaction with smectites were determined by the kinetics of Al-Ferron reaction colour development. The composition of the Al species retained by smectites was not the same as that present in the original solution added. The slow-reacting complexes present in the solution were preferentially adsorbed by dioctahedral smectites. Smectites prepared from slow-reacting polymer solutions showed changes in interlayer separation, b–dimension, order along the c axis and spectroscopic properties, after storage at room temperature. The OH-Al Cheto-type montmorillonite prepared from both solutions showed more retention of Al, best stability at room temperature and after thermal treatment at 550°C than interlayered OH-Al Wyoming-type montmorillonite and OH-Al beidellite smectites.

Natural aluminosilicates can contain Fe in tetrahedral or octahedral coordination. Amongst smectites, tetrahedral iron is known to occur in Fe-rich nontronites but few indications exist for the presence of tetrahedral Fe in smectites of the montmorillonite–beidellite series. A set of 38 different bentonites showed a correlation of tetrahedral charge and Fe content in their smectites. All materials with large tetrahedral charge were rich in Fe. This could be explained by a general tendency of Fe to enter the tetrahedral sheet. To investigate this correlation, nine materials were selected and investigated by Mössbauer, UV-Vis, Fe K pre-edge and EXAFS spectroscopy with respect to tetrahedral Fe (Fe[IV]). The latter two methods were at the detection limit but Mössbauer and UV-Vis spectroscopy provided consistent results indicating the significance of both methods in spite of some scatter caused by the overall small amount of tetrahedral Fe. The results indicate the absence of any relation between Fe content and tetrahedral Fe. Tetrahedral Fe can be present in Fe-poor smectites and absent in the case of Fe-rich materials. This means that Fe-rich montmorillonites have a larger tetrahedral charge which is not caused by Fe[IV] but by Al[IV]. A possible explanation for this indirect relation is based on: the coordination of Al3+ in the weathering/smectite-forming solutions determines the coordination in the precipitates; and the Al[IV/VI] ratio increases with increasing pH. The correlation could thus be explained if the pH of weathering solutions generally was higher in Fe-rich parent smectite rocks than in more acidic smectite parent rocks. The relation between tetrahedral charge and Fe content can probably be explained by different geochemical contexts throughout the formation of smectites which affect the coordination of dissolved Al.

Dioctahedral smectites are clay minerals that widely used as a crucial component for the edifice of natural barriers in industrial wastes and wastewater treatment. The hydration behaviours of these mineral types are very sensitive by environmental surroundings changes. The present work focuses the evolution of the interlayer water amount as a function of the relative humidity rates (RH), varied along a humidifying-drying cycle, in the case of two dioctahedral smectites with different charge location (i.e. Wyoming montmorillonite SWy-2 and Beidellite SbId-1). The CEC (i.e. cation exchange capacity) of the studied sample is saturated by two monovalent cations (i.e., Cs+ and Na+) characterized by a different ionic radius. The X-ray diffraction (XRD) profile modelling tools based on the indirect method that consist on the comparison of experimental 00l reflections with other calculated from structural models is used to perform these aims. The qualitative XRD profile investigation suggests heterogeneous hydration behaviour at different stage of the cycle for all studied samples. The water content fluctuation, confirmed by the appearance of a hydration hysteresis, within the interlamellar space of diverse complexes is an irreversible process during the shrinking–rewetting sequence. Comparing to Na+ cations, the presence of the Cs+ ions in exchangeable sites of both smectite structures is accompanied by more orderliness of systems, which retunes the lowest water molecules amount over the applied cycle.