Mineral–organic matter (OM) associations play an important role in determining the long-term retention of OM in soils. However, the retention mechanisms of OM in cation–mineral–OM systems remain unclear. Taking into account the dominance of montmorillonite (Mnt) in the soil of the temperate zone, we investigated the stability of humic substances (HSs) in the Fe(III)–Mnt–HS system using thermal analysis. The HS degradation started at ~387°C in the Fe(III)–Mnt–HS system, which was higher than that of the Fe(III)–HS system (290°C). The formed ferrihydrite (Fhy) mainly contributed to the enhanced labile OM retention through adsorption and/or co-precipitation, whereas Mnt inhibited the initial formation and subsequent transformation of Fhy, thus improving the stability of OM. These results suggest that the HS stability in Fe(III)–clay–HS systems depends on the Fe speciation affected by clay minerals, and this finding provides insights into OM–mineral interactions in temperate-zone soils.

To solve the problem of the leakage of phase-change materials and expand the application of clay minerals in the field of phase-change materials, illite and paraffin wax were used for the first time as a new binary hybrid core material with silica as the wall material. Phase-change microcapsules were prepared using the sol–gel method and successfully applied in silicone rubber foams. Differential scanning calorimetry showed that the microcapsules had a melting temperature of 62.99°C and a latent heat capacity of 98.24 J g–1, indicating their good heat-storage capacity. Furthermore, the effectiveness of using illite as a filler for preventing paraffin leakage was demonstrated through 200 thermal cycling tests, which demonstrated a leakage rate of only 2.6% compared to 3.2% exhibited by microcapsules without illite.

Three clay materials (codded MY3, KG and KK) from western Cameroon were selected and investigated for the production of refractory bricks. Samples MY3 and KG are kaolinite-rich materials, having clay mineral contents of 88% and 72%, respectively, whereas KK is a sand-rich material with a total clay content of 44%. Chamottes were prepared using each clay, and the ground chamottes were later used in the refractory formulation, with each raw clay used as a binding phase. After firing, the X-ray diffraction analyses of all of the refractory bricks indicated the same mineral assemblage made of quartz, cristobalite and mullite. The cristobalite is due to high-temperature conversion of quartz, whereas the mullite is due to clay mineral conversion. The evaluation of the linear shrinkage, physical properties (including bulk density and open porosity) and mechanical testing through refractoriness under load and compressive strength indicates that all of these clays could be used as raw materials for standard clay refractory materials. These results stand as a proof for the potential for these locally available materials to be used as raw materials for refractories that could be locally produced to reduce the cost of access to refractory raw materials faced by industries located in Cameroon.

The retreat of the Dead Sea and the lowering of the base level in recent decades have led to the exposure of the littoral clay sediments on the shore, the occurrence of exposed mudflats and the development of ground subsidence along strips (‘subsidence strips’) and clustered sinkholes. Based on field observations and laboratory analyses, the present study characterizes the clayey sediments in the environment of the exposed mudflats on the western Dead Sea shore. The clayey sediments of the exposed mudflats (‘mudflat sediments’) consist of fine-grained laminated calcareous clays. The mineral composition of the bulk mudflat sediments consists of clay and carbonate minerals (calcite, aragonite and dolomite) with some quartz and feldspar, and frequently gypsum and halite. The clay mineral composition of these samples is smectitic illite–smectite and kaolinite with some discrete illite and palygorskite. The smectitic illite–smectite is randomly interstratified (1.7 nm illite–smectite type R = 0). Although the detrital smectitic illite–smectite in the mudflat sediments is situated in the saline environment of the Dead Sea shore, no significant illitization is observed in the depositional detrital clay. Subsidence strips with clustered sinkholes were formed in the exposed mudflats as part of the adjustment of the Dead Sea periphery to the lowering of the base level as a result of the retreat. The field observations in the studied area reveal that the subsiding of mudflat sediments in the formation of the subsidence strips usually involves mud sagging of wet clayey sediments in the subsurface and sediment collapse of dry clayey sediments near the surface.

Natural tuff samples in western Anatolia (Türkiye) originating from Miocene rhyolitic–pyroclastic rocks with >80 wt.% heulandite/clinoptilolite zeolites were investigated for their surface characteristics determined according to nitrogen adsorption after degassing at 150°C (specific surface area, pore volume and pore diameter). Additionally, these surface characteristics were correlated with the cationic compositions of the heulandite/clinoptilolite group minerals. The examined samples were characterized by two main pore diameters that were not related to specific surface area and pore volume but were partially related to the types and occupancy of extra-framework cations. One set of samples has a pore diameter of ~24 Å, total cation content (Na + K + Ca + Mg) ranging from 3.46 to 4.40 and a (Na + K)/(Ca + Mg) ratio ranging from 0.34 to 0.92. The total cation contents and (Na + K)/(Ca + Mg) ratios of the remaining samples with a pore diameter of ~37 Å are 4.30–5.08 and 1.48–2.85, respectively. After degassing at 300°C, there is a slight difference in the pore diameters of these two sets of samples (~37 and 38 Å). The pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio < 1 (heulandite composition) increased from 24 to 36–38 Å with increasing degassing temperature, whereas the pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio > 1 (clinoptilolite composition) increased from 37 to only 38–39 Å. However, there is no correlation between the Si/Al ratios and the cation-exchange capacities of the samples and their surface characteristics obtained by degassing at the two temperatures.

Illite is a common clay mineral that is found in a wide range of geological settings. The good thermal stability and non-swelling properties of illite make it valuable in ceramic materials, paints and coatings, drilling fluids, agriculture and geological studies. To gain a deeper understanding of the physical and chemical properties of illite, in the present paper the atomic and electronic structures of a typical trans-vacant 1M Al-rich illite were constructed and calculated using density functional theory. The calculated indirect band gap of Al-rich illite was 4.99 eV. The electronic analysis revealed that the interactions in the tetrahedral sheet were more stable than those in the octahedral sheet. The substitution of Al atoms noticeably reduced the stability of the tetrahedral sheet in Al-rich illite. Other properties of Al-rich illite, including the density of states, electron population/charge, electronic charge density and bonding interaction, are also discussed and analysed in detail.

Nine halloysite nanotubes (HNTs) have been examined using scanning electron microscopy (SEM), atomic force microscopy (AFM) and (cross-sectional) transmission electron microscopy (TEM) to evaluate details of their external and internal morphologies. The samples span morphologies within the cylindrical to prismatic-polygonal framework proposed by Hillier et al. (2016). The ‘carpet roll’ model assumed in the conceptualization of most technological applications of HNTs is shown to be far too simplistic. Both cylindrical and prismatic forms have abundant edge steps traversing their surfaces that, by analogy with plates of kaolinite, correspond to prism faces. The mean value for the diameter of the central lumen of the tubes is 12 nm. Numerous slit-like nanopores, with diameters up to 18 nm, also occur between packets of layers, particularly in prismatic forms at the junction between a central cylindrical core and outer packets of planar layers. These pores expose aluminol and siloxane surfaces, but unlike the lumen, which is assumed only to expose an aluminol surface, they do not extend along the entire length of the nanotube. Edge steps seen most clearly by AFM correspond in height to the packets of layers seen in TEM. TEM cross-sections suggest that tube growth occurs by accretion of a spiralled thickening wedge of layers evolving from cylindrical to polygonal form and reveal that planar sectors may be joined by either abrupt angular junctions or by short sections of curved layers. A more realistic model of the internal and external morphologies of HNTs is proposed to assist with understanding of the behaviour of HNTs in technological applications.

The synthesis of nano-silica is gaining the attention of researchers due to its numerous applications in various fields such as medicine, the food industry, catalysis, agriculture and construction, amongst others, because of its unique physicochemical features. However, achieving its facile synthesis and finding inexpensive source material that is locally available requires further exploration for its large-scale production. This paper reports the synthesis and characterization of nano-silica from locally available laterite clay using the sol-gel method. The product was analysed using X-ray florescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. It was observed that the product was spherical, agglomerated and amorphous in nature. The obtained nano-silica was found to have 97% and 95% purity for sodium hydroxide and potassium hydroxide, respectively. The synthesized nano-silica is expected to play pivotal role as a pozzolanic activator in the construction industry.

Dodecyl dimethyl benzyl ammonium (DDBA) is a novel cation surfactant used to modify clay minerals. DDBA-intercalated montmorillonite is formed by the ion exchange between DDBA cations in the solution and cations in the montmorillonite interlayers. By using molecular dynamics simulations, we investigated the basal spacings, interlayer structures and dynamics of DDBA-montmorillonites. The results showed that the calculated basal spacings agreed well with experimental values and that the layering behaviours of DDBA had been revealed. The ammonium groups of DDBA ions preferred staying close to the centre of Si–O six-member rings. The benzyl group and lauryl group were oriented in parallel in the monolayer state, whereas they were tilted in other states. DDBA ions have very low mobility in the interlayer region, indicating that the negatively charged montmorillonite surfaces can effectively fix this positively charged surfactant. The microscopic structures and dynamics obtained in the present study provide atomic-scale insights into the properties of DDBA-intercalated clay minerals.