Six samples of ‘Vermiculite’ have been studied to investigate the mechanism of its well known but poorly understood property to exfoliate. The samples were analysed quantitatively by XRD to determine their precise mineralogical composition. Electron microprobe methods, including elemental mapping of native potassium and of caesium (introduced by cation exchange) were used to examine variation in the chemical composition of the particles. Most of the samples examined show heterogeneous mineralogical compositions which occur as distinct zones within the volume of individual particles, presenting a mosaic texture. Exfoliation is related to this mosaic distribution of the different mineral phases within the particles. Lateral phase boundaries between vermiculite and mica layers, or vermiculite and chlorite layers are postulated to prevent or impede the escape of gas from a particle, resulting in exfoliation when the pressure exceeds the interlayer bonding forces that hold the layers together. This mechanism provides a common explanation for the exfoliation of ‘Vermiculite’ by thermal methods or by treatment with H2O2. Paradoxically, one sample which consists of pure vermiculite, in the mineralogical sense of the term, demonstrates that pure vermiculite does not and should not exhibit the property of exfoliation. Our explanation of the mechanism of exfoliation explains the commonly observed particle size dependence of exfoliation and the tendency for obviously poly-phase ‘Vermiculite’ samples to show the largest coefficients of expansion.

Intercalation of cationic surfactants hexadecylpyridinium (HDPy+) and hexadecyltrimethylammonium (HDTMA+) into the interlayer space of homoionic (Na-, Ca- and Zn-) smectites by solid-solid reactions was investigated. These reactions were complete within 15 min. Changes in the surface and structure of the smectites modified with different surfactants were characterized using XRD, FTIR and DSC. The intercalation of surfactant is controlled by the exchangeable cation of smectite and monofunctional ammonium cation type. HDPy+ and HDTMA+ surfactants were retained by Zn-exchanged smectite, suggesting important surface properties (CEC = 80 meq/100 g clay, SBET = 116.5 m2/g) and acid-base properties (point of zero proton charge PZC, density charge σH). HDPy cation loading was effective, suggesting that the aromatic polar group is favoured for intercalation. Comparing with original clay, modification with surfactants increased the basal spacings d001. Based on the d001 spacing of modified smectites, different configurations of surfactants within smectite interlayer were proposed as a function of surfactant concentration, which were examined by FTIR and DSC.

The purpose of this paper was to prepare purified Na- bentonite with improved properties for use in the pharmaceutical industry. Calcium bentonite from the Shagia region of Karak district, Pakistan, was activated with various proportions of sodium carbonate (2, 3, 5 and 8 wt.%) and purified by sedimentation to remove impurities, especially quartz. X-ray diffraction (XRD), and swelling volume confirmed the conversion of raw bentonite to sodium bentonite by using 5% Na2CO3. The sodium bentonite (K5) obtained by activation met the chemical and microbiological requirements set by the pharmacopeias regarding the toxic trace elemental content (Pb and As), absence of E. coli, total aerobic microbial contents and physicochemical properties such as swelling volume, pH and sedimentation volume. Therefore K5 bentonite could be designated as potentially suitable for pharmaceutical applications. The CEC, surface area, porosity, pH, gel formation and swelling volume indicated that K5 bentonite could be used in the formulation of oral suspension and in topical application.

The influence of Zn on the adsorption and desorption of Cry1Ab toxin from Bacillus thuringiensis (Bt) on palygorskite and montmorillonite was studied. The adsorption of the toxin gradually increased with increasing Zn concentration from 0 to 1.0 mmol L–1, and then decreased with further increase in Zn concentration. The adsorption isotherms of the toxin in the absence and presence of Zn were well described by the Langmuir equation (R2 > 0.9810–0.9991). The separation factor (RL) decreased with increase of Zn concentration, suggesting that the irreversibility of the adsorption increases. The XRD results showed that the treatment by Tris buffer or Zn(NO3)2 solution caused an expansion of the interlayer space of montmorillonite but did not affect palygorskite. The IR spectra suggest that Zn was likely to be combined with amino groups on the surface of the toxin. The presence of Zn during the adsorption of the toxin decreased desorption, suggesting that the residual risk of toxin would be exacerbated if soil is polluted by zinc.

The experimental data on adsorption of Fe and CN of a ferrocyanide complex onto raw and acid-activated clinoptilolite/sepiolite on the basis of detention time and particle size was modelled by a linear and a non-linear approach. The linearized best-fit isotherm selection method and non-linear error minimization was applied through Freundlich, Langmuir and Temkin isotherms. ERRSQ, MPSD, HYBRID and ARE error functions were minimized by a developed MATLAB script to determine the isotherm parameters in non-linear optimization. The complex was not adsorbed as whole anions but the Fe and CN were adsorbed separately. 0.65 mg Fe/L. min and 4.84 mg CN/L. min initial adsorption rates were achieved with acid activated clinoptilolite. The Fe adsorption was not as successful as CN. The adsorption of Fe and CN was described by Freundlich and Langmuir isotherms respectively. The differences between the predicted isotherm parameter sets of linear models and minimized error function models indicated that both the best-fit isotherm selection and the isotherm constant determinations can be performed properly by error minimization as well as by conventional linear best fit modelling approach.

The removal of enrofloxacin, a fluoroquinolone antibiotic, from aqueous solution by adsorption onto bentonite was investigated in this study. The effects of initial concentrations, contact time and temperature on the adsorption of enrofloxacin were studied via batch experiments. The adsorption equilibrium was achieved within 60 min for all studied concentrations. The adsorption capacity increased with the increase of initial concentration within a concentration range. Higher temperatures were favourable for the adsorption. The change of Gibbs free energy (ΔG°), change of enthalpy (ΔH°) and change of entropy (ΔS°) were evaluated and the results indicate that the adsorption should be an endothermic and spontaneous process. The Langmuir isotherm model fitted to the experimental data better than the Freundlich model. The adsorption follows the pseudo-second order kinetic model.

The ability of montmorillonite to mitigate the toxic effect of heavy oil from the Nakhodka oil spill, by growth of hydrocarbon-degrading bacteria and enable bioremediation was studied. Montmorillonite enhanced the bacterial growth significantly (P < 0.05) in the main treatment containing heavy oil+bacteria+montmorillonite (OBM), because the specific growth rate (μ) was greater than that in the biotic control treatment containing heavy oil+bacteria (OB). Significant amounts of Si and Al (major constituents of montmorillonite) were not released in the aqueous phase over the ∽24-day experiment (P > 0.05). Transmission electron microscopic observation showed that the hydrocarbon-degrading bacterial cells were covered and encrusted with montmorillonite particles. Scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS) also showed that the surrounding of the bacterial cells was frequently rich in Si but not in Al. Fourier transform infrared (FTIR) spectroscopy indicated that the heavy oil-bacterial cell-montmorillonite particle complex retained the composition of both water and heavy oil. X-ray powder diffractrometery (XRD) analysis revealed that heavy oil and heavy oil-bacteria did not change the basal spacing of montmorillonite over a period of 24 days. The enhancement of hydrocarbon-degrading bacterial growth is attributed to montmorillonite likely serving as both bacterial growth-supporting carrier and protective outer layer against high concentrations of heavy oil that inhibit growth. These results shed light on the interactions in oil-bacteria-clay complexes and could potentially be used in marine oil spill bioremediation.

Clayey deposits of Nanga-Eboko (central Cameroon) were studied to assess their potential as building materials. Characterization was performed using XRD, FTIR, XRF, DTA/DTG and firing testing. Clays appear as discontinuous pockets with the same textural characteristics in three villages located on both sides of the Sanaga River. The average thickness of the exploitable layer is about 3m. The estimated tonnage ∼7–17×105 m3 can supply a brick industry of great importance. SiO2 (∼70%), Al2O3 (∼15%) and Fe2O3 (∼4%) are the predominant oxides of the natural clays. Quartz (∼55%), kaolinite (∼33%), illite (∼5%) and K-feldspar (∼4%) are major minerals. Clays are not suitable for building construction due to their fine-grained size and high plasticity properties. Firing properties of bricks (950 and 1050°C) are good despite the high shrinkage values. Therefore the addition of “degreasers” is recommended to control shaping and drying.