This study evaluates the rare earth element (REE) geochemistry in altered trachyandesitic ignimbrites, tuff and lava flows in the Hashtjin area by assessing chondrite-normalized REE patterns and Y/Ho geochemical ratios. Modifications in the REE patterns took place along altered fault zones that were affected by hypogene and supergene alterations. The precursor volcanic and pyroclastic rocks contain phenocrysts of plagioclase accompanied by augite, zircon, apatite and pyrite. Based on X-ray diffraction analysis, the main mineral assemblages of the altered units consist of kaolinite as the main clay mineral, SiO2 polymorphs (quartz and cristobalite) and anatase as a minor constituent. The chondrite-normalized REE patterns of argillic samples reveal fractionation of light REEs (LREEs) compared to heavy REEs (HREEs), together with a marked Eu anomaly and a weak W-type tetrad effect related to the weak non-charge radius control (CHARAC) behaviour of REEs and slightly higher Y/Ho and Zr/Hf ratios. The relationship between the Y/Ho and Zr/Hf ratios and recognizable T3 and T4 effects (tetrad effect) suggests that an increasing degree of water–rock interaction occurred during hypogene alteration processes by acidic hydrothermal fluids that were overprinted by supergene alteration. Water–rock interaction and adsorption by Mn-oxides and clay minerals are considered to have played important roles in determining the close to non-CHARAC behaviour of REEs during the argillic alteration of the pyroclastic rocks in the Hashtjin area.

Drilling fluids are essential for the operation and productivity of petroleum wells. This study compares the efficiency of a salted water-based mud for which the viscosity has been enhanced with polymeric compounds with that of a new salted water-based mud containing palygorskite clay, which mainly functions as a viscosity enhancer. The experiment measured the density, apparent viscosity, plastic viscosity, yield point, American Petroleum Institute filtrate and pH of the samples. The results indicate that the rheological properties of the fluids containing greater amounts of palygorskite were not affected significantly by the addition of salt. However, when the concentration of palygorskite was low, the rheological behaviour of the samples was appropriate to the drilling operation only with lesser amounts of salt. In addition to its good rheological properties, the filtrate volume obtained for samples containing greater concentrations of palygorskite was lower, which suggests that the filtration properties at the bottoms of the wells were controlled appropriately.

Potential secondary influences on titanium distribution should be evaluated when using ash beds as volcanic source indicators and for correlation purposes. In this study, well-correlated altered ash beds in Permian–Triassic boundary (PTB) successions of various facies in South China were investigated to better understand their use in source discrimination and stratigraphic correlation. The ash beds deposited in lacustrine and paludal facies contain significantly more Ti relative to deposits in marine facies. Neoformed anatase grains nanometres to micrometres in size are associated closely with clay minerals, whereas detrital anatase was observed in the remnants of altered ash beds of terrestrial facies. Extraction of the clay fraction of altered ash beds may exclude significantly detrital accessory minerals such as anatase and rutile added during sediment reworking, and the concentrations of immobile elements in the clay fraction may therefore be used to interpret more effectively their source igneous rocks.

In 2019, BYK Additives (Widnes, UK; www.byk.com) marked the 55th anniversary of the discovery by Dr Barbara Zsusanna (Susanna) Neumann of the extraordinary product known as Laponite®. The range of Laponite® products developed in the UK during the early 1960s is one of the first examples of truly nanodimensional materials manufactured on an industrial scale, at a time when the field of nanotechnology was only being hinted at (Feynman, 1959). These hectorite-like synthetic nanoclays with very unusual properties have been an enduring commercial success for the UK company that first patented and introduced them to the market, Laporte Industries, which is now a part of the BYK company. The Laponite® brand has proved tremendously popular with academic and industrial scientists worldwide, being cited in >3000 patents and >2500 published academic articles.

Clay often has severe detrimental impacts on cement-based materials. Therefore, it is necessary to investigate the mechanism causing the deterioration to improve the service life of cement-based materials. Based on accurate dimensional analysis, a mechanism that influences clay is proposed: the intercalation of the side chains of superplasticizer molecules in the interlayer space of the clay. To lessen this harmful effect, a new clay-resistant admixture (CRA) possessing cationic groups of small molecular size was synthesized through a novel dimensional design. The length and width of the side chains of this superplasticizer molecule were 9.50–17.50 and 0.25–0.40 nm, respectively, with a radius of ~3.74 nm in solvent, which is larger than the interlayer spacing of montmorillonite (i.e. 1.09–2.14 nm). The longitudinal and latitudinal lengths of the CRA molecule were 0.468 and 9.456 nm, respectively, ensuring intercalation in the interlayer of montmorillonite. The increase in interlayer spacing of the clay was 0.364 nm following addition of polycarboxylate superplasticizer (PCE) plus CRA and 0.632 nm following addition of PCE, which suggests that the CRA plays the role of a ‘sacrificial agent’ that is preferentially intercalated into the interlayer space of clay to further prevent the side chains of the superplasticizer molecules from entering the interlayer. The aim of this study was to propose a suitable means of synthesizing a new CRA to address the impact of clay through dimensional design and mechanism analysis, which contributes to the theoretical study and technological improvement of cement-based materials.

The influence of excess Al2O3 on 3:2 mullite produced from α-Al2O3 and pyrophyllite powder was examined. A mixture consisting of 28 wt.% dehydroxylated pyrophyllite and 72 wt.% α-Al2O3 was milled in an attrition mill. The milled powders were sintered by spark plasma sintering (SPS) at 1600°C for 10, 20 and 30 min. Subsequently, the samples were heated at 1350°C for 2 h to determine the influence of the excess Al2O3 on the microstructure. No glassy phase was detected in the sample containing 72 wt.% Al2O3 and sintered at 1600°C for 20 min. The sample with 72 wt.% Al2O3 had greater hardness and fracture toughness compared to 3:2 mullite. The greatest hardness and fracture toughness of 12.43 GPa and 2.71 MPa m–0.5, respectively, were obtained in the sample containing 72 wt.% Al2O3 sintered at 1600°C for 20 min.

The adsorption behaviour of the herbicide clomazone on inorganic and organically modified montmorillonite from the Bogovina deposit in Serbia was investigated. Montmorillonite was modified first with NaCl and then with organic complexes such as hexadecyltrimethylammonium bromide (HDTMA) and phenyltrimethylammonium chloride (PTMA). Changes in the surface properties and morphology of the montmorillonite before and after the modification with various concentrations of organic complexes were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Adsorption of clomazone on all examined samples was investigated using the batch adsorption method. Montmorillonite modified with HDTMA-bromide displayed greater uptake of the clomazone compared to the PTMA-montmorillonite, and both organically modified montmorillonites displayed greater uptake of the herbicide compared to the inorganic montmorillonite. Comparing the Freundlich coefficient and maximum adsorbed clomazone quantity values obtained by Langmuir model, the levels of adsorption of clomazone decreased in the following order: HDTMA-montmorillonite with 1.00 cation-exchange capacity (CEC) saturation > HDTMA-montmorillonite with 0.75 CEC saturation > PTMA-montmorillonite with 1.00 CEC saturation > PTMA-montmorillonite with 0.75 CEC saturation > HDTMA-montmorillonite with 0.50 CEC saturation > HDTMA-montmorillonite with 0.25 CEC saturation > PTMA-montmorillonite with 0.50 CEC saturation > PTMA-montmorillonite with 0.25 CEC saturation > Na-montmorillonite > raw sample. The type and content of an organic cation plays an important role in the behaviour of clomazone in a solid/liquid system. It is concluded that organically modified montmorillonite from Bogovina might be used as an effective adsorbent for clomazone.

Six clays from various deposits were studied for their use in the production of structural clay products. The clays were characterized using chemical (X-ray fluorescence), mineralogical (X-ray diffraction) and thermal (differential scanning calorimetry/thermogravimetry) analyses. Particle-size distribution was determined by laser diffraction, plasticity by the Pfefferkorn method and the residue by the sieve-size method. Next, specimens were formed by extrusion and characterized by their linear thermal shrinkage (on drying and firing), water absorption, bulk density, porosity and compressive strength. The clays were, in general, suitable for the manufacture of structural ceramics, mainly bricks. The clays from flooded pits (AV1 and AV2) were classified as floodplain clays and alluvial clays. The clays mined in mountainous regions (AM1 and AM2, as well as AV1) were characterized as siliceous clays due to the abundance of free SiO2 phases.

This study focuses on the characterization, thermal behaviour and firing properties of clays from Cap Bon Basin, Tunisia. Chemical (inductively coupled plasma atomic emission spectroscopy) and mineralogical (X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy) characterization of the clays was carried out. Physical properties were identified using particle-size distribution and Atterberg limits tests. Differential thermal analysis/thermogravimetry, dilatometry, XRD and FTIR analyses were conducted to assess the thermal behaviour, transformations and crystalline phase development during firing. The clays studied show large proportions of silt and clay fractions. They are rich in SiO2, Al2O3 and Fe2O3 and mostly consist of illite, kaolinite, smectite and minor mixed-layer illite-smectite. Associated minerals are mainly quartz, calcite and feldspar. To monitor the firing properties, three clay mixtures referred to as M1, M2 and M3 were prepared according to the physicochemical and mineralogical characteristics of the raw clays. These were sintered at 900°C, 1000°C and 1100°C and tested for firing shrinkage, flexural strength and water absorption. As a result, various mineralogical transformations occurred at 900–1100°C associated with the crystallization of new phases. The main transformations identified at >1000°C resulted in the formation of anorthite and mullite, causing significant densification of the fired ceramic materials. Sintering at 1100°C increased the densification and thus improved the flexural strength. At this temperature, the sintered ceramic tiles exhibited excellent properties, namely water absorption of 2–3% and flexural strength of 30–41 MPa, indicating that these studied clays might be used as raw materials for the production of stoneware tile ceramics.

Two samples collected from the phosphogypsum deposits of the chemical products industry Elixir Prahovo (Serbia) were subjected to a recrystallization experiment performed over several repeated cycles. In these tests, phosphogypsum was separated into recrystallized (purified) gypsum, insoluble residue and supernatant. Both raw phosphogypsum and recrystallized gypsum were examined using inductively coupled plasma optical emission spectrometry, X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry. The activity concentrations of 238U, 235U, 226Ra, 210Pb, 232Th and 40K were investigated using γ-ray spectrometry. Based on the activity concentration results, a number of radiometric parameters were calculated for the original and recrystallized phosphogypsum (i.e. radium equivalent activity, γ indices for construction materials, α index and external and internal hazard indices). Raw phosphogypsum samples showed greater mean activity concentration levels of 238U and 226Ra than the international recommended limits, while the recrystallized gypsum demonstrated notably lower activity concentrations for these two isotopes. The activity concentration of 226Ra in recrystallized gypsum is ~6 times lower than in raw phosphogypsum. Therefore, recrystallized gypsum does not present a radiation hazard when used as a building material, while raw phosphogypsum meets the requirements only for road construction materials.

A Na-montmorillonite (Na-MMT) was activated with HNO3 (20 wt.%) solution at various temperatures and times to obtain acid-activated MMT (Acid-MMT). Zinc (4 wt.%) was supported on Acid-MMT via the impregnation method using Zn(NO3)2⋅6H2O as a precursor. The catalytic performance of the Zn/Acid-MMT for the aromatization of heptane was investigated. The amount and distribution of acidity of Acid-MMT, which could be adjusted by changing the acid activation time and temperature, significantly affected the heptane conversion and aromatics content. As a result, an efficient Zn/Acid-MMT catalyst for the aromatization reaction was obtained by optimizing the acid-treatment conditions of Na-MMT.

Brushite (CaHPO4.2H2O) is an important calcium phosphate encountered in bone tissue engineering and bone cement formulation. There are many studies on the synthesis and characterization of brushite, but full-scale substitution and replacement of Ca by Sr in brushite as a key element in medical and environmental applications has not yet been explored systematically. Therefore, this study aims to evaluate the effects of substitution of Ca by Sr on the microstructural and thermal properties of brushite, including the chemical phases present, crystallization, structural water and phase stability. The chemical phases were determined by means of powder X-ray diffraction. The thermal properties were studied by thermogravimetric analysis. Crystallization and surface morphology were analysed using scanning electron microscopy. Various properties were dependent on the incorporated Sr ions. The replacement percentage of Sr may be divided into two major stages: the first from 0% to 50%; and the second from 50% up to 100%. The (CaxSr1–x)HPO4.nH2O shows that micro-scale crystals of platy brushite formed in the first stage of Sr replacement, from 0% up to 50%. As Sr might inhibit the formation of crystals, crystal nucleation rates were reduced as the Sr percentage increased. An amorphous product formed as a result of 50% Sr replacement. The second stage of Sr replacement with Sr contents >50% yielded a new crystal morphology corresponding mainly to SrHPO4.nH2O. The complete replacement of Ca by Sr transforms the brushite with platy microcrystals into SrHPO4 nanosheets.

The adsorption and retention of phosphates in soil systems is of wide environmental importance, and understanding the surface chemistry of halloysite (a common soil clay mineral) is also of prime importance in many emerging technological applications of halloysite nanotubes (HNTs). The adsorption of phosphate anions on tubular halloysite (7 Å) has been studied to gain a greater understanding of the mechanism and kinetics of adsorption on the surface of HNTs. Two well-characterized tubular halloysites with differing morphologies have been studied: one polygonal prismatic and one cylindrical, where the cylindrical form has a greater surface area and shorter tube length. Greater phosphate adsorption of up to 42 μmol g–1 is observed on the cylindrical halloysite when compared to the polygonal prismatic sample, where adsorption reached a maximum of just 15 μmol g–1 compared to a value for platy kaolinite (KGa-2) of 8 μmol g–1. Phosphate adsorption shows strong pH dependence, and the differences in phosphate sorption between the prismatic and cylindrical morphologies suggest that phosphate absorption does not occur at the same pH-dependent alumina edge sites and that the lumen may have a greater influence on uptake for the cylindrical form.

The Tamusu region in northwest China is a key candidate area for China's clay rock deep geological repositories (DGRs) for high-level radioactive waste (HLRW) as it is composed of a continuous layer of thick lacustrine mudstone. To evaluate this mudstone as a host rock, two special test boreholes were drilled to investigate its spatial distribution and mineralogical and hydraulic characteristics. The southwest boundary and depositional centre of the lake basin were well delineated by boreholes TZK-1 and TZK-2. The continuous single-layer thickness of the target mudstone formation was up to 300 m at a depth of 500–800 m. Three main mineral types were determined, namely carbonates (mainly dolomite and ankerite), analcime and albite, and their abundance was used to distinguish three different facies. Other mineral phases, such as clay minerals (mainly illite and kaolinite), pyrite, hematite, quartz and calcite, were present as admixtures. The presence of carbonates may increase the mechanical strength and analcime may enhance the radionuclide adsorption properties of the mudstone. The self-sealing properties, which may be affected by the small amount of clay minerals, remain to be investigated. The hydraulic conductivity of the mudstone determined via in situ pulse tests ranged from 10–13 to 10–10 m s–1, suggesting that the Tamusu mudstone has ultra-low permeability. The transmissivity of the Tamusu mudstone fluctuated in regions with varying lithologies, but remained relatively constant for consistent lithologies. In summary, these preliminarily results confirm the possible suitability of the target formation as a host rock for DGRs of China's HLRW.

The objective of this work was to use air-dried sepiolite granules as an additive in cigarette filter tips to increase the removal yield of tar and nicotine from mainstream smoke. Granules with a mass of 95 mg per cigarette filter and a mean particle size (D) of 0.05–0.41 mm were used to constrain the effects of the mean particle size and mass of sepiolite in the removal process. The granules were sandwiched in common cellulose acetate filter tips. Maximum removal yields of 90% were obtained when D ≤ 0.10 mm. Filters containing granules with a mean size of 0.10 mm and mass variations from 35 to 95 mg were tested, and increasing amounts of sepiolite added led to progressively greater yields of tar and nicotine from 20% to 90%. The sepiolite granules were examined using scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy and X-ray diffraction techniques both before and after smoke experimentation. It is suggested that tar and nicotine were condensed both on the fibre clusters of the sepiolite granules and in the voids between them during the flow of the mainstream smoke.

Several generations of chamosite, including a red variety, occur in the Ordovician hydrothermalized oolitic ironstone from Saint-Aubin-des-Châteaux (Armorican Massif, France). Their chemical re-examination indicates a low Mg content (0.925 < Fe/(Fe + Mg) < 0.954), but a significant variation in IVAl. Minor vanadium is present at up to 1.1 wt.% oxide. Variations in IVAl, the vanadium content and the colour of chamosite are related to the hydrothermal reworking of the ironstone. Taking into account other published data, the ideal composition of chamosite is (Fe5–xAl1+x)(Si3–xAl1+x)O10(OH)8, with 0.2 < x < 0.8 (0.2: equilibrium with quartz; 0.8: SiO2 deficit). The red chamosite (IIb polytype) has a mean composition of (Fe3.87Mg0.23Mn0.01□0.07Al1.74V0.07)(Si2.33Al1.67)O10(OH)8. This chamosite is strongly pleochroic, from pale yellow (E || (001)) to deep orange red (E ⊥ (001)). Visible–near-infrared absorbance spectra show a specific absorption band centred at ~550 nm for E ⊥ (001), due to a proposed new variety of Fe/V intervalence charge-transfer mechanism in the octahedral sheet, possibly Fe2+ – V4+ → Fe3+ – V3+. While the formation of green chamosite varieties is controlled by reducing conditions due to the presence of organic matter as a buffer, that of red chamosite would indicate locally a weak increase of fO2 related to oxidizing hydrothermal solutions.

The interaction between a basic dye, rhodamine B, and a separated fine fraction from natural clay was studied. Chemical analysis, X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the predominance of beidellite in the fine clay fraction. The interaction of rhodamine B with the fine clay fraction showed that sorption was fast and followed a pseudo-second-order kinetic model. The comparison between sorbed rhodamine B amounts as a function of the various experimental parameters such as pH, sorbent mass, dye concentration and the presence of competing ions suggests that: (1) the sorption process is largely pH-dependent; (2) significant competition is observed between the dye and the Ca2+ and Mg2+ ions; (3) the sorption proceeds, principally, by a cation-exchange mechanism; and (4) the sorption capacity of the fine fraction in the presence of competing cations such as Ca2+ is ~0.28 mmol g–1.