Dacitic andesitic calc-alkaline lavas and their pyroclastic rocks of Upper Cretaceous age are widespread in the Ordu area, eastern Black Sea Coast of Turkey. Ca-bentonite and Ca/Nabentonite deposits with significant economic potential formed in the broader region. The mineralogy and geochemistry of these deposits were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analyses. The parent rocks (PR) and bentonite samples were analysed for the major and trace element contents, including rare-earth elements, to understand the effect of differential alterations on element mobility. The bentonites contain mainly di-octahedral Ca-montmorillonite with minor amounts of illite, quartz, calcite, dolomite and feldspar. Primary K-feldspar and plagioclase phenocrysts were altered in the bentonite horizons, and were completely leached at greater depth. For this reason, the higher quality bentonites are found at deeper zones. Bentonite horizons are characterized by relatively high loss on ignition (LOI: 9.8–20.8%) and MgO content (3–5%) and low K2O (<0.5%) and Na2O (<2%) contents compared with the least altered parent rocks. Silicon, Ca, Mg, Mn and P are markedly enriched whereas Fe, Na, K and Ti are depleted in the bentonite samples. The chondrite-normalized rare earth element (REE) patterns show identical trends characterized by strong light rare earth element (LREE) enrichment in both the PR and bentonite samples. The LREE contents are higher than those of their heavy counterparts (HREE) in the samples. Alteration of the PR to bentonite is associated with intense chemical leaching and subsequent removal of K and Na in open-system conditions.

Sudoite, an aluminium-rich di-trioctahedral chlorite, is known primarily from highgrade diagenetic/ low-temperature metamorphic Al-rich rocks and from hydrothermal deposits in Alrich terrains. This contribution reports a rare occurrence of pore-lining sudoite in Permian red beds from the eastern part of the Southern Permian Basin. Sudoite is a ubiquitous mineral in aeolian sandstones of the Eastern Erg, a large dune field buried in the subsurface of the Fore-Sudetic Monocline, SW Poland. Sudoite crystals are arranged in a honeycomb texture and often associated with high-porosity intervals. It is concluded that sudoite crystallized at the expense of early diagenetic dioctahedral smectite at a temperature lower than 180°C under the influence of hot, Mgrich and K-poor fluids, which migrated from a basement and/or deep part of the basin upward through permeable aeolian sandstones and mixed with colder pore solutions. Tosudite was a likely intermediate phase in the smectite to sudoite conversion.

The distribution of Al3+ and Fe3+ between octahedral and tetrahedral sites of dioctahedral smectites was shown to be controlled by a partition coefficient Kd(4/6) = [(Fe3+)4×(Al3+)6]/[(Fe3+)6×(Al3+)4]. The Kd(4/6) value is near 0.006 for natural dioctahedral smectites, formed between 2 and ~100°C, and near 0.0174 for smectites synthesized at 200°C. These Kd(4/6) values, obtained from both chemical and spectroscopic data, were consistent with those calculated using the ionic radii of cations and Brice’s model (Brice, 1975). The partition coefficient approach explained well why for natural and synthetic dioctahedral smectites no tetrahedral Fe3+ is detected when the total Fe3+ content is below 3 atoms per unit cell (24 oxygen atoms).

A kaolin clay was activated with 1.0 M H2SO4 solution at minimum liquid to solid ratio (L/S) using microwave heating. The optimum experimental conditions for activation were L/S ratio 3.0 mL 1 M H2SO4 per gram kaolin, microwave input power 500–600 W, and heating time 5–10 min. Activation at L/S < 3.0 mL/g using 1.0 M H2SO4 was not efficient, indicating the influence of solvent for absorbing microwaves more intensively and thus improving activation. Significant physicochemical changes were observed by the proposed procedure with smaller volumes of activator compared to the conventional heating method. Microwave input power and heating time have a strong influence on the quality of the final material; activation at high input power (>700 W) and longer heating times (>10 min.) are not recommended since they cause dissolution of kaolinite structure. Microwave-heated kaolin manifested better adsorption for tartrazine dye due to improvements in textural and chemical properties of kaolinite. Moreover, irradiation of used kaolinite has significantly improved dye desorption, increasing the importance of microwaves in regeneration/recycling studies. Detailed dielectric measurements of kaolin-acid mixtures recorded at frequencies much lower than 2.45 GHz revealed that absorption of radiation is highly dependent on the activator solution in the mixture. For 3.0 mL/g mixtures, high dielectric constant ε’ 5223, dielectric loss factor ε” 5083, tangent loss tan d 1.30, penetration depth dp 0.57 cm at (103 Hz), and AC-conductivity σ 0.032 Om–1 were determined at 105 Hz. Filling the pores of kaolin by acid solution increased the microwave absorption and hence de-alumination of kaolinite.

Organo-bentonites were prepared using a bentonite and an aqueous cetyltrimethylammonium hydroxide solution. The ratio of the surfactant (in mmoles) to the cation exchange capacity varied from 0.5 to 20, with 20 being the highest ratio ever reported in the literature. At high surfactant to cation exchange capacity ratios, the interlayer spacing increased to 3.75 nm due to the formation of a paraffin-type bilayer of surfactant cations, which was shown to be mainly in gauche conformations using solid state 13C CP/NMR. When the exchange reaction was carried out in a methanol-water mixture, the expansion of the organo-bentonites depended on the concentration of methanol (% by volume). The decomposition temperatures of the organic cations depended on the basal spacing of the organo-bentonites, and in situ X-ray diffraction revealed that the basal spacing of our organo-bentonites was stable up to 210°C. Above this temperature, the basal spacing shrunk to 1.47 nm due to decomposition of the surfactants.

In the present study, changes of iron content, brightness, particle size, mineralogy and paramagnetic properties of kaolins before and after superconducting high gradient magnetic separation (SHGMS) were investigated. The Fe2O3 contents of the feed decreased by 56% after 3.5T SHGMS with 1# steel wool, but higher magnetic intensity to 5.5T did not remove additional iron. The ISO brightness of the kaolin sample after SHGMS was improved from 56.9% to 76.7%. The D50 value of the magnetic rejects was 35% larger compared to the feed. Large particles might block the micro-pores in the steel wool matrix. Compared to the feed, the dark or red impurities significantly decreased in the non-magnetic product. Paramagnetic species in the kaolin sample were sensitive to SHGMS. The resonances at g = ~2.0 and g = 4.0 decreased significantly in the concentrate compared to the feed in the ESR spectra. Iron components in the non-magnetic product were more likely to be non-paramagnetic. The results are useful for understanding the SHGMS in kaolin treatment, and might be a guide for optimizing process parameters.

In order to improve the optical properties and enhance the stability of Zn1–xCdxS nanoparticles, which are important optoelectrical materials, the ternary Zn1–xCdxS nanoparticles were enclosed in a layered octosilicate by a three-step process, namely (i) protonation of Naoctosilicate, (ii) ion-exchange in order to introduce Zn and Cd ions into the interlayer space, and (iii) addition of S2– to form Zn1–xCdxS particles in the interlayer space of the octosilicate. The basal spacing (~10 Å) of the final ZnCdS-Oct-n (n = 1, 2, 3, 4) composites noticeably increased in comparison with that of the precursor H-Oct (7.5 Å). This may be attributed to the incorporation of larger size Zn1–xCdxS particles into the interlayer space of H-Oct. The UV-visible spectra of the composites suggested that the transmission band-edges gradually shifted to low energy with increasing molar ratio of Cd/Zn. Moreover, the transmission band-edges of the composites are between those of layered Octosilicate, ZnS, and CdS. TEM observation confirmed that the size of Zn1–xCdxS nanoparticles enclosed in the layered silicate was about ~3–5 nm.

The composition, morphology and crystal order of clay minerals in silt-sized sediments carried in suspensions from 25 major rivers across tropical southern Africa have been studied by X-ray diffractometry and scanning and transmission electron microscopy. Our goal was to determine the spatial variability of clay-mineral associations in diverse geological settings, and in climatic conditions ranging from humid Angola and Zambia to hyperarid Namibia and the Kalahari. Specific attention was paid to the micromorphology and chemical composition of smectite particles. The relative abundance of smectites, illite/mica, kaolinite and chlorite enabled identification of regions characterized by different physical and chemical processes: (1) negligible chemical weathering is documented in Namibia, where river muds mostly contain illite/mica or smectite derived from Damara metasedimentary or Etendeka volcanic rocks; (2) kaolinite documenting intense weathering, reaches a maximum in the Okavango, Kwando and Upper Zambezi, sourced in subequatorial Angola and Zambia; (3) suspended-load muds in the Limpopo and middle Zambezi catchments display intermediate features, with varied assemblages and smectite compositions reflecting diverse parent lithologies. Clay mineralogy and chemical composition are confirmed as a most effective tool to unravel present and past climatic conditions on a continental scale.

The application of natural fertilizer mixtures that improve nutrient retention ability of soils has attracted considerable attention in recent years. In addition to rock phosphate (RP), the basic components of these mixtures are zeolites modified with selected cations, such as the ammonium ion. The NH4-zeolite serves as a carrier of nutrients as well as a soil conditioner, and it promotes the RP dissolution in all soil types. The purpose of the present work was to prepare costeffective NH4-zeolite supplement, using 32 full factorial experimental designs, with concentration of modifier and processing time as variables. Saturation processes were carried out on two types of natural zeolites, K- clinoptilolite (K-Cp) and Ca-clinoptilolite (Ca-Cp). The Response Surface Method (RSM) was applied for evaluation of cation exchange, suggesting an effective NH4+ modification of natural zeolite at lower quantities of modifier than commonly found in other studies on the topic. Using Principal Component Analysis (PCA), differences between samples relative to the process variables were clearly outlined and correlated with concentrations of the exchanged cations. The best results were obtained for the K-Cp type modified with 1.5 M solution of ammonium sulfate (at a Cp/NH4+ stochiometric ratio 1:7.5) for all three processing intervals. By optimizing the modification process parameters, an experimental design of partially saturated NH4-Cp supplement that has the potential to supply all major plant nutrients was proposed.

The purpose of this study was to determine whether a bentonite from the Gafsa deposit (western Tunisia) could be used to remove the Foron Blue 291 (FB) azo dye from wastewater. Batch adsorption and desorption experiments were conducted using untreated and purified bentonite and the influence of contact time, pH, adsorbent mass and temperature of the dye solution on the adsorption of FB was evaluated. Kinetic and isotherm data were fitted using two non-linear kinetic and two non-linear isotherm equations. In addition, the fits were evaluated using the coefficient of determination (R2) and the RMSE. The percentage of dye removal increased with increasing amount of adsorbent until total discolouration was achieved. The adsorption isotherms followed the Langmuir model, with the purified bentonite having a higher adsorption capacity than the raw material due to its higher specific surface area. In addition, the FB molecules were removed from the liquid medium by physical adsorption. Batch desorption experiments were conducted to study the desorption kinetics and the characteristics of the desorption isotherms as well as to quantify the portion of the FB (by mass) that was irreversibly fixed on the solid. Overall, the desorption kinetics were similar to the adsorption kinetics, which indicated that the adsorption-desorption process of azo dye is non-singular; irreversibility occurred that was underlined by an observed thermodynamic index of irreversibility (TII) of 0.69–0.94. The desorption isotherms of the FB depended on the mass of the FB that was initially adsorbed on the bentonite sample, suggesting hysteresis. The amount of irreversibly retained FB was between 46 and 68% of the initial adsorbed mass.