The formation of iron-rich phyllosilicates can occur at different natural or engineered settings. In this study, the influence of pH in the hydrothermal synthesis of iron-rich phyllosilicates was investigated in the pH range 8.50–12.10 after the ageing of the precursor. The synthesized samples were characterized by powder X-ray diffraction, Raman and Mössbauer spectroscopies and transmission electron microscopy. Three domains of pH were identified, and these correlated with silica availability and its speciation in the solution. The formation of 1:1-type FeIII/FeII phyllosilicate was observed between pH 9.67 and 10.75. Above pH 10.75, two types of phyllosilicate-like mineral phases were observed. In addition to 1:1-type FeIII/FeII phyllosilicate, 2:1-type FeIII/FeII phyllosilicate was observed. Below pH 9.67, mainly amorphous silica and iron oxides were observed. The findings show that pH governed the crystallinity and nature of the obtained phyllosilicate-like phases.

Acid activation was carried out by heating muds prepared from Ca-rich bentonite (CaB), sulfuric acid (H2SO4) and distilled water, yielding various bleaching earths (BEs). The roles of each of the process variables, namely mass fraction of H2SO4 (x) in the dried CaB and pure H2SO4 mixture, heating temperature (T) and contact time (t), in the activation were tested. The raw CaB and each BE were examined with X-ray diffraction, chemical analyses, N2 adsorption/desorption, pH-metry and tintometry. The BE contents in both the aqueous and oily suspensions were set to 2% by mass in order to measure the pH value and the bleaching power, respectively. The optimum conditions for the activation to obtain a BE having the same bleaching power (0.60) as Tonsil® Optimum Bleaching Earth for soybean oil were determined as x = 0.35, T = 100°C and t = 2 h. The bleaching power increased only marginally upon increasing the activation time from 2 h up to 10 h at a given x and T. After 10 h, significant changes did not take place in the bleaching power of the BE. The mass fraction of total structural metal oxide (y), pH value, specific pore volume (V), specific surface area (S) and mean internal diameter (D) of the mesopores for the optimized BE are y = 0.10, pH = 3.0, V = 0.31 cm3 g–1, S = 225 m2 g–1 and D = 7 nm. The pH and D values were more important for bleaching the alkaline refined soybean oil compared to the other parameters tested.

Disposal of Finnish spent nuclear fuel is planned to be based on the KBS-3 repository concept. The role of the bentonite buffer in this concept is essential, and thus the behaviour of the bentonite has to be known. The experiments in this paper concentrated on providing information about the effects of carbon dioxide CO2(g) partial pressure on compacted sodium bentonite, giving an insight into the buffering capacity. The experimental setup consisted of a hermetic box which had a CO2-adjusted atmosphere, and the bentonite was in contact with this atmosphere through water reservoirs. The results indicated that it is possible to measure online the changing pH in the porewater inside compacted bentonite using IrOx electrodes. It was found that the pH fell if the CO2 partial pressure increased above atmospheric conditions. The experimental results indicated a greater fall in pH than in our model in the test cases where CO2 was present. The pH in the experiment with 0 PCO2 remained nearly constant throughout the 5 month period. On the other hand, the pH dropped to near 6 with 0.3 PCO2 and to 5.5 with 1 PCO2.

A genetic classification of clay rocks is given in which five main types are recognized. In this classification minerals of the kaolin group formed directly from hydrothermal solutions, along with sulphides, sulphates, and pneumatogenic minerals, are separated from the same minerals formed by the hydrothermal-metasomatic action of gases and vapours on aluminosilicate rocks. Some data on the occurrence of these two types in Azerbaijan are recorded. The origin of the bentonitic clays (“gilabi”) of Azerbaljan is also discussed; the geology of the deposits indicates cycles of volcanic activity and long-range transport of volcanic ash.

The pyroclastic carbonatitic rocks from the Catanda volcanic area (Angola) contain annite and phlogopite grains which have been affected to a significant extent by vermiculitization. A mineralogical study of these micas has revealed that the annite was altered to K-vermiculite while vermiculitization of phlogopite generated Ca-vermiculite. Intermediate alteration products such as intergrowths of phlogopite/Ca-vermiculite were also found, but interstratified crystals of phlogopite/ vermiculite, a common intermediate product during vermiculitization processes, are not reported in the Catanda rocks. The two types of vermiculitized micas show ‘accordion’ textures, related to the expansion of vermiculite. To the authors’ knowledge, the present study is the first report of expanded vermiculites described in natural rocks and not generated as a consequence of industrial processing.

High-whiteness kaolinite mining reserves are scarce. In some locations, it is necessary to remove material to access them (adding to the cost). Therefore, processes have been developed to eliminate contaminants, such as iron, and provide alternatives to the used contaminated materials that, after being treated, meet quality criteria. In our previous research, we developed an electrochemical process for kaolin whitening at the laboratory level and bench scale, demonstrating the reaction mechanisms that occur during the removal of iron from kaolin. However, the geometry used at the laboratory level does not present the most suitable position for the electrodes. Therefore, in the present study, we focused on the geometry and the function of the electrodes. This is necessary during the escalation process to reach the pilot-scale level. The study was carried out using computer-aided engineering in the COMSOL Multiphysics computer program and by analysing the distribution of the electric potential and the electric current of the geometries considered while performing the scaling. The results indicated that the change in the anode position from perpendicular to parallel to the discs improved the distribution of electric current density on the cathode surface and so increased the elimination of iron through electrochemical deposition. Similarly, to reduce the amount of material used in the construction of the reactor, the anode-size effect was analysed, revealing that relatively small anodes improved the distribution of electric current density over the entire surface of the electrode and not only at the edges.

Two clays of the kaolinite type, one from Bihar and the other from Kerala, were each separated into particle-size fractions greater than and smaller than 1·4 µ.e.s.d. X-ray diffraction, differential thermal analysis, cation-exchange capacity and moisture absorption determinations and chemical analysis of the fractions showed that the micaceous mineral was concentrated in the fine fraction of one whereas it was mostly in the coarse fraction of the other. The evidence suggests that the mineral in the former belongs to the illite group and in the latter to the mica group.

Two novel modified montmorillonite (Mnt) components were prepared using Mnt nanoparticles and two surfactants: docosyl-trimethylammonium chloride (BTAC) and sodium dodecyl sulfate (SDS). These modified Mnts were used to remove a carcinogenic and harmful dye, crystal violet (CV), from solution. Optimization and modelling studies of the adsorption of these two modified Mnts were performed using response surface methodology. Four influential variables (concentration of adsorbent, temperature, pH and CV concentration) were studied to obtain the optimum conditions for CV removal. The optimal values of these variables for the two modified Mnts yielded 100% dye-removal efficiency. The optimum conditions for CV adsorption on Mnt-BTAC and Mnt-BTAC-SDS, respectively, are temperatures of 25.00 and 33.29°C, pH values of 9 and 10.1, CV concentrations of 50.00 and 10.44 mg L–1 and adsorbent concentrations of 1.00 and 0.98 g L–1. In equilibrium studies of the two modified Mnts, the Temkin isotherm was selected as an appropriate model, and in kinetic studies of these Mnts, the fractal-like integrated kinetics Langmuir model was found to be the best model. The Mnt-BTAC-SDS component is an affordable adsorbent with high adsorption capacity for CV.

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.

Exchangeable cation associations in physical mixtures of bentonite and laponite have been examined using X-ray diffraction and a combination of electron microprobe analysis and multivariate statistical methods. The results suggest that cation exchange can occur in air-dry mixtures when pressure (∼64 kbar) is applied. Although no attempt is made to describe the mechanism of the reaction it appears to require the presence of adsorbed water.

The study of M and Mg ion exchange (M = Co, Ni, Cu, Zn), between silicate gels SiO2.q(M, Mg)O.nH2O and amino acid (glycine) saline aqueous solutions (M, Mg)SO4, shows that the introduction of the complexing agent completely upsets the original distribution equilibria of M and Mg between the two types of phases. The values of the measured bulk distribution coefficient

are lowered considerably relative to the inorganic reference distribution coefficients. The lowering of D may be accounted for by calculating the contents of the different species, MA, MA+, M2+, under which the metallic element M is present in the solutions. The values of

resulting from the calculated M2+ contents are identical to the values of Dref, determined in systems without a complexing agent.

Clay minerals possess the peculiar characteristic that they normally occur as very small crystals. We cannot, therefore, afford to ignore the contribution that colloid science can make to the study of clay minerals. Many colloidal systems are stable because the particles are electrically charged. There is, of course, electrical neutrality of the system as a whole, but there is an electric separation within the system whereby electricity of one kind (it may be a positive or negative, depending on the system) is anchored for the time being to the particles while the complementary charge exists as ions (counter ions they are often called). Some of the counter ions must be regarded as in solution in the suspending medium (normally water) for it is their mobility relative to the particles which gives rise to electrical conductivity and to electrophoresis, electro-endosmosis and streaming potential.

The Weissenberg method has been used to study crystalline fragments of hydrobiotites from Stupná near Křemže, Czechoslovakia. The intensity distribution for basal reflections recorded in zero-level photographs indicates that most ‘single crystals’ are nearly regular interstratifications of vermiculite and biotite. Proportions of vermiculite in these interstratifications lie between 12 and 60%.