In this study, the adsorption of NH3 gas on a bentonite from Ünye (Turkey) in its natural state and after acid treatments, was investigated experimentally at 298 K and up to 100 kPa. Bentonite was treated with HCl solutions of various concentrations (0.5–2.5 M) at 75°C for 4 h. X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption and thermogravimetric/differential thermal analysis (TG/DTA) were used to characterize the bentonite before and after acid treatment. The quantitative XRD analysis demonstrated that the bentonite sample was composed predominantly of smectite (75%), with abundant feldspar (20%) and minor opal-CT, analcime and quartz (5%). Increasing gas adsorption values of acid-treated bentonites were analysed depending on the structural changes of the clay. The NH3-adsorption capacities of the bentonite samples (3.801–5.068 mmol g–1) were also compared with previously studied clay-based materials (0.828–4.000 mmol g–1) in terms of their textural and structural differences.

Three clay minerals from southern and central Tunisia were characterized. Both XRD quantitative analysis and a chemical method were used to determine the mineralogical and physico-chemical characteristics of the <2 μm clay fractions. The XRD, CEC and specific surface measurement analyses showed that the dominant phase in all samples is illite-smectite with kaolinite and traces of quartz also present. From quantitative XRD, the abundances of the minerals identified are consistent with the measured CEC, specific surface area and TG/DTA properties. Analysis by XRD also showed that the illite-smectite phases are composed of thin stacks (two to a maximum of ten layers per stack) of random illite-smectite and ordered (R1) illite-smectite. There is also some discrete illite.

Few reports exist on the use of Diffuse Reflectance Infrared Fourier Transform Spectrometry coupled with Mass Spectrometry (DRIFTS-MS) in situ to monitor the dehydroxylation of kaolinitic clays. The use of DRIFTS-MS in situ allows study of the effect of heat treatment on the dehydroxylation, identifying intensities and temperatures at which the hydroxyl groups are released, forming metakaolinite and meta-alunite. The effluent gases from the infrared cell were analysed by mass spectrometry. The decrease in intensity of the bands at 3694, 3669, 3650 and 3621 cm−1 associated with the −OH stretching vibration modes of AlVI−OH−AlVI of kaolinite began at 450°C. Two additional bands at 3513 and 3485 cm−1 are associated with the vibration of AlVI−OH of alunite that also began to disappear during thermal treatment. Monitoring of the fractions m/e 17 and 18 using a mass spectrometer revealed that the intensity of these fractions increased starting at 450°C. Therefore, it is possible to study the dehydroxylation process of clays during thermal treatment.Chemical and mineralogical characterization of a kaolinitic clay (KN) fromMexico showed that the clay consists of 64.8% kaolinite, 11.0% alunite and 24.4% quartz based on PXRD, EDS, TG/DTA, TEM and FTIR results, and suggested that the material might have potential for use in the manufacture of ceramics, refractory bricks or geopolymers.