The study analysed 93 samples from four Serbian clay deposits to determine their suitability for ceramics production. The samples were mainly composed of illite and kaolinite. Ternary diagrams were used to classify the samples and evaluate their applicability. Winkler's diagrams, ternary graphs and mineralogical compositions were analysed. The results showed a broader area in these graphs than previously determined for structural ceramics, as well as the potential of these clays for ceramic production. The study used dry-milled, hydraulically semi-dry, pressed and fired samples to assess water absorption and flexural strength and statistical analysis to determine the key parameters influencing final product quality, including that of refractory, wall and floor tiles. This paper evaluates the raw clay materials’ applicability in ceramic production, promoting sustainable use through rapid initial tests, energy savings through dry milling and ecologically sound principles through resource-efficient evaluation.

Acidified suspensions of Al-saturated kaolinite, montmorillonite, mica, illite, and biotite in 10−3 M NaNO3 were potentiometrically titrated with 0.1 N NaOH and 0.1 N HNO3 in succession in a CO2-free nitrogen atmosphere. The resulting curves were compared with those for Al(NO3)3 solutions of similar Al concentration in the supernatant solution and corrected for Al in the entrained solution in the clay.

Base titrations of Al ions adsorbed on all the minerals, except montmorillonite, showed two pH inflections separated by a buffering range. With montmorillonite, there were three pH inflections similar to those for Al in solution. The first inflections in the titration of suspensions occurred at lower pHs and were less pronounced than for Al in solution. These represent the titration of H3O+ sorbed during the pretreatment. The buffering by adsorbed Al ions is also less than that by Al in solution.

The OH− used up by adsorbed Al ions between the first and last inflections was equal to, or slightly greater than, the CEC of the minerals, except for mica where it was more than twice the CEC, because new interlayer surfaces were formed during the acid pretreatment. Acid titration curves of Al ions in the adsorbed and solution states showed hysteresis when related to the base titration curves. The use of two titration speeds (3 and 0.3 pH units/hr) only slightly affected the titration curves of the minerals suggesting that the observed effects were not caused by lack of equilibrium with added base or acid.

Boron adsorption by Ca forms of montmorillonite, illite, and kaolinite was determined as a function of pH and boron concentration in solution. Data from batch experiments were compared with results computed for each clay according to fitted adsorption coefficients (maximum boron adsorption and affinity constants related to the binding energy). The agreement between calculated values and experimental results indicates that a phenomenological equation can be used to predict boron adsorption on clays as a function of both of these variables. For the solution-to-clay ratios examined, the water content does not affect the boron-surface interaction as expressed by the above adsorption parameters. Because the affinity of clays for B(OH)4− is much stronger than for B(OH)3 , the adsorption maximum was obtained only under alkaline conditions at approximately pH 9.0 to 9.7. It is suggested that the pH of maximum adsorption is a function of the ratios of affinity coefficients of the three species B(OH)3, B(OH)4−, and OH− competing for the same adsorption sites. The adsorption coefficients indicate that in some cases the difference in the amount of adsorbed boron between montmorillonite and kaolinite could be either small or large, depending on the circumstances. The main factor that would affect this difference is the total amount of boron in the suspension. Estimated value of the adsorption maximum was 2.94, 11.8 and 15.1 µmole/g for Ca-kaolinite, Ca-montmorillonite, and Ca-illite, respectively.

X-ray intensity ratios of Si/Al, Si/Fe, and Al/Fe in micron-sized particles of geochemical standards were found to vary linearly with the composition ratio. The same linear relationship was found for samples of the clay minerals kaolinite and illite.

The effects of hydrothermal conditions on the sorption and fixation of cesium by various clay minerals and shales were investigated. Hydrothermal heating, which may be expected in a radioactive waste repository, altered the clay minerals and shales and led to a decrease in their cation-exchange capacity. Cesium sorption greatly decreased in micaceous vermiculite and in well-crystallized illites containing vermiculite upon hydrothermal treatment at 400°C and 300 bars pressure due to complete layer collapse. However, poorly crystallized illites heated as above showed either a small increase or only a slight decrease in Cs sorption because of partial layer collapse. These studies show that the decrease in Cs sorption is greater in well-crysallized illites than in poorly crystallized illites when treated similarly under hydrothermal conditions. Hydrothermal heating of Cs-sorbed and Cs-saturated samples increased the amount of Cs fixation in all minerals and shales as a result of collapse of the layers. For example, a sample of the Conasauga shale fixed only 18% of sorbed Cs before treatment but fixed 47% after hydrothermal treatment at 200°C and 300 bars pressure. Thus, hydrothermal conditions in a shale repository may be beneficial after leaked radioactive Cs ions are taken up by clay minerals in shales.

The adsorption-desorption of the cationic pesticide chlordimeform from aqueous solutions on montmorillonite, kaolinite, illite, and vermiculite appears to be a cation-exchange process coupled with the coadsorption of neutral molecules and the extraction of Al from the structure of the mineral. Chlordimeform adsorption on montmorillonite, illite, and vermiculite by cation exchange is an irreversible process, whereas chlordimeform adsorbed on kaolinite is weakly bonded to the clay and easily removed by washing with water. X-ray powder diffraction and infrared spectroscopic data show that chlordimeform cations are adsorbed in the interlamellar spaces of montmorillonite at charge sites, lying in a flat position in contrast to kaolinite, illite, and vermiculite, where they adsorb on external surfaces or charge sites close to the crystal edges.

Clay samples from shales and bentonites in the Mancos Shale (Cretaceous) and its stratigraphic equivalents in the southern Rocky Mountain and Colorado Plateau have been analyzed by X-ray powder diffraction methods. The major clay in the shales is mixed layered illite/smectite, with 20–60% illite layers. The regional distribution of ordered vs. random interstratification in the illite/smectite is consistent with the concept of burial metamorphism in which smectite interlayers are converted to illite, resulting finally in ordered interstratification. The interstratification data correlate with other geologic information, including rank of coal and Laramide tectonic activity. In addition, contact metamorphism of the shale by Tertiary igneous intrusions produced a similar clay suite. Chemical variation within these shales (particularly the presence or absence of carbonate) affected the clay conversion reactions in the interbedded bentonites and the shale itself during the early stages of transformation. In extreme cases, shales and bentonites from a single outcrop may contain clays that range from pure smectite (calcareous shales) to ordered illite/smectite containing ⩾50% illite layers (noncalcareous shales). The use of mixed-layered illite/smectite compositions to infer thermal regimes, therefore, may be misleading unless allowance is made for local chemical controls.

The rates of release of Al by M NH4NO3 (pH 3) from minerals saturated with Al ions at pH 3 suggest that Al ions migrated from the surface layers and the matrix cores of kaolinite, montmorillonite, illite, and biotite, but only from the matrix core of muscovite mica. From the 0.25–0.5 μm kaolinite and montmorillonite, part of the ‘surface’ Al is released ‘instantaneously’ and the rest by first order kinetics, but the coarse 1.5–2.5 μm kaolinite has only the former component. From illite and biotite, ‘surface’ Al is released by ‘bulk diffusion’ kinetics suggesting the existence of disturbed peripheral layers of finite thickness. The diffusion coefficients, Dm, for the matrix core follow the trend: mica ≃ biotite > illite > montmorillonite > kaolinite.

Based on models proposed in previous work, the ionic composition of the ‘surface’ Al is calculated. This shows that (1) this composition varies according to the mineral from 3 to 100% Al3+, the remainder being in the hydrolyzed form, and (2) the apparent hydrolysis constants are different for each mineral and significantly different from those of Al ions in solution.

The thickness of the two-layer ethylene glycol complex of dioctahedral smectites varies under room conditions between 17.3 and 16.5 Å because of such factors as layer charge density, type of interlayer cation, and relative humidity. Neglecting this variability can give up to 30% error in the X-ray powder diffraction estimation of the smectite:illite ratio of the mixed-layer structures. Three methods have been developed for the interpretation of X-ray powder diffraction patterns of glycolated mixed-layer illite/smectite which take layer-spacing variability into account. The methods include a technique for quantifying the degree of layer ordering. In addition, the proposed techniques minimize the error due to the influence of domain size on positions of reflections. The experimental error can be kept below 5% or below 1% smectite layers, depending on the method applied, provided that the peak positions are measured with the accuracy of ± 0.02°2θ.

Mixed-layer illite/smectite (I/S) clays in lower Eocene sediments of the Texas Gulf Coast decrease in expandability with depth as found in previous studies of clay diagenesis, but at the same depth the 1/S clays from sand laminae tend to be more expandable than clays from adjacent shales. The I/S clays with greater expandability from sands collapse to phases with very low expandabilities after saturation with K. This non-ideal smectite behavior indicates that many of the expandable layers in I/S clays from sand laminae possess an illite-level negative layer charge on the structure. The Greene-Kelley Li-saturation test of the I/S clays also reveals that a considerable portion of the increased layer charge deficiency is created by tetrahedral substitution. The illitization of individual smectite layers in an I/S clay is envisioned to be a two step process instead of the single step rapid transformation implied in many earlier studies. The first rate-limiting step is the creation of sufficiently large negative layer charge in the lattice, primarily by AI for Si substitution in the tetrahedral sheet. The second rate-limiting step is the supply of K to the high-charged expandable layers. The abundance of high-charged expandable layers in I/S clays from sand laminae suggests that the K supply is influenced more by competing ions in the interstitial waters than by the absolute activity of K.

To identify mineral alterations which might occur in stream environments, predominantly illitic soil clays were equilibrated in bottom sediment environments under natural and laboratory conditions for 217 and 98 days, respectively. Changes occurring after 217 days on the bottom of the Auglaize River, Ohio, consisted of a reduction in carbonate content, a decrease in particle size, and a slight loss of Al and Si; however, no significant changes in basal spacings were observed.

Clays equilibrated in river water under laboratory conditions at 4° and 25°C in CO2, N2, or air atmospheres showed only an increase in oxalate-extractable iron. The concentrations of Al, Si, Fe, Mn, K, and Ca in solution above the clays varied with the atmosphere and temperature. The concentrations of Fe, Al, and Si in solution may have been influenced by the dissolution of amorphous Al-Fe-Si compounds. Therefore, the mineralogical differences between soils in the watershed and sediments in the drainage system can not be attributed to mineralogical transformations during residence in the drainage system.

Cretaceous bentonites were collected in outcrop from the Sweetgrass Arch and the Disturbed Belt in Montana. The mixed-layer illite-smectite (I/S) components of the bentonites from the Sweetgrass Arch have from 0 to 25% illite layers and no detectable structurai Fe2+, whereas the samples from the Disturbed Belt have from about 25 to 90% illite layers, and all contain Fe2+. A positive correlation (r = 0.89) exists between the percentage of structural iron that is Fe2+ and the amount of fixed interlayer K in the I/S.

The higher percentage of illite layers in the samples from the Disturbed Belt is attributed to reactions related to elevated temperatures caused by burial beneath thrust sheets. The increase in Fe2+/Fe3+ with increasing percentages of illite layers is tentatively attributed to a redox reaction involving the oxidation of organic matter. Although there is no statistical evidence for an increase in octahedral charge with an increase in illite layers when all the samples are considered together, iron reduction may have contributed as much as 10 to 30% of the increase in total structural charge that occurred in any given sample during metamorphism. The remaining structural charge increase can be attributed to the substitution of Al3+ for Si4+ in the tetrahedral sites.

Mixed-layer illite/smectite (I/S) was formed by reacting the Chambers or Polkville montmorillonite hydrothermally at 270° and 350°C from several hours to more than 15 weeks. Reactions were conducted in closed vessels containing K or mixed K-Na, K-Ca, or K-Mg solutions of varying concentrations. The reaction rate and the rate of ordering of I/S for the reaction smectite + K+ → mixed-layer I/S + SiO2 was inhibited by the addition of Na+ Ca2+, and Mg2+; the inhibitory strength of Na+, Ca2+ and Mg2+, on an equivalent basis, increased approximately in the ratio 1:10:30. The first order reaction-rate constants for the reactions at 270° and 350°C indicate an activation energy of about 30 kcal/mole.

In the experimental system studied, the reaction smectite → mixed-layer I/S appeared to proceed by solid state transformation, as suggested by: (1) rapid dissolution of large amounts of silica, probably creating an Al-enriched residue; (2) similarity of particle size and morphology of the mixed-layer products to those of the original montmorillonite, implying no extensive dissolution of Al3+; and (3) relatively high activation energy compared to published values for silicate dissolution.

Adenosine-5-phosphates (ATP, ADP, AMP) are adsorbed by clay minerals at very low concentrations (≤2 mg/liter). In contrast to quartz, the clay minerals exhibit a strong preference for ATP over AMP. The experimental data are expressed as recovery rates (adenosine-phosphate in solution to total nucleotide added). For example, the recovery rates of ATP, ADP, and AMP in the presence of sodium montmorillonite are 0,17, and 100%; in the presence of quartz 95, 100, and 99%. The recovery rate of AMP on clays is markedly decreased by the presence of ATP, that is, ATP increases the adsorption of AMP by cooperative interactions.

A part of ATP not recovered in the equilibrium solution is dephosphorylated to ADP. For example, 45% of ATP not recovered in equilibrium solution with calcium montmorillonite is recovered as ADP; with sodium montmorillonite only ADP can be recovered in solution.

Two variables must be considered when calculating exchange free energies (ΔG°ex) for 2:1 clays: (1) anionic field strength, as expressed by equivalent anionic radius (ra), and (2) interlayer water content, as expressed by interlayer molality. For smectites that are in a state of high hydration, interlayer molality is determined by the cations undergoing exchange. Thus ΔG°ex for an exchanging cation pair can be calculated solely from measurements of ra. ra is related to layer charge per half unit cell (C) and ab unit cell area (A) by: ra = (-A/8πC)1/2. The layer charge necessary for cation fixation can be predicted by calculating the ra at which cation exchange with an illite structure expresses a AG°ex equal to that of exchange with a smectite structure. The theory can also be applied qualitatively to understand the high selectivity of illite for Cs+, the fixation of K+ rather than Na+ in shales during diagenesis, the stability of illite over muscovite in the weathering environment, and cation segregation in smectite.

The immobilization of soluble Cs from spent fuel elements by ion exchange and direct chemical reaction with clay minerals or shales was investigated under hydrothermal conditions. Various clay minerals or shales were reacted with likely Cs sources and water at 300 bars pressure and 100°, 200°, and 300°C for 4, 2, and 1 months, respectively. Pollucite was the principal product, but CsAlSiO4 was also observed, along with unreacted or hydrothermally altered aluminosilicates. From Cs concentrations of the product solutions partition of Cs between liquid and solids was found to vary depending on the Cs source, the clay or shale phase, temperature, and run duration. For example, illite-Cs2MoO4 interactions resulted in 19, 32, and 95% fixation of added Cs at 100°, 200°, and 300°C respectively. Fixation of as much as 97% of the Cs in some solids was observed. In addition to Cs-aluminosilicates, Cs was fixed on cation-exchange sites by interlayer collapse in montmorillonite. Reactions with Cs2MoO4 also produced powellite because Ca was available in the reaction mixture. The U6+ from β-Cs2U2O7 was reduced to form uraninite by sulfide- and/or organic-rich shales. (Cs,Na)2(UO2)(Si2O5)3·4H2O, an analog of weeksite, was produced in reactions with β-Cs2U2O7. The reaction products pollucite and uraninite can immobilize much of the Cs and U from spent fuel elements because Cs in pollucite is extremely difficult to exchange and U in uraninite is insoluble.

The nature of Cr(NH3)63+ and Cr(en)33+ (en = ethylenediamine) adsorbed on chlorite, illite, and kaolinite has been studied by X-ray photoelectron spectroscopy (XPS). The interaction of the chromium complexes with the clays began at pH 3. During the 7-day interaction time the pH of the complex-clay suspension increased to 8 for illite and chlorite. For kaolinite the pH increased to about 3.6 with Cr(NH3)63+ and to 6.4 with Cr(en)33+. These pH changes appear to be associated with a clay-catalyzed hydrolysis of the chromium-amine complexes. XPS binding-energy data for adsorbed chromium indicate that the dominant species are chromium aqua complexes. Nitrogen/chromium atom ratios, calculated from the XPS photopeak intensities, are less than 6:1 for complexes adsorbed on the clays, suggesting that chromium complexes are initially adsorbed but subsequently hydrolyze to produce aqua-chromium surface species.

The impact of temperature on the migration of cations within layers of clay minerals is of profound significance for the design and practical application of materials derived from clay minerals. This study focuses on Li+ and Na+ as representative cations, together with illite (Ilt) and montmorillonite (Mnt) as representative clay minerals. The study investigates the behaviour of cation migration and occupation within clay minerals across varying temperatures. A series of samples were prepared meticulously by immersing illite and montmorillonite in Li+ and Na+ solutions, subsequently subjecting them to different temperatures (unheated, 100, 150, 200, 250 and 300°C) for 24 h. Through the use of techniques such as X-ray diffraction (XRD), cation exchange capacity (CEC), Fourier-transform infrared spectroscopy (FTIR), magic angle rotating solid nuclear magnetic resonance spectroscopy (MAS NMR), and X-ray photoelectron spectroscopy (XPS), the study discerns structural transformations in illite and montmorillonite, and tracks the migration and occupation of Li+ and Na+. The findings reveal that following heating, Na+ and Li+ do not infiltrate the lattice of illite. For montmorillonite, Na+ also does not migrate into the montmorillonite lattice, however, in contrast, Li+ does exhibit migration into this lattice. Notably, the migration and occupation of interlayer Li+ within montmorillonite exhibit discernible temperature dependence. Specifically, upon reaching 150°C, interlayer Li+ migrate to ditrigonal cavities within the tetrahedral layers. As the temperature elevates to 200°C, Li+ further permeate vacant octahedral sites through the ditrigonal cavities, culminating in the formation of a localised trioctahedral structure.

Microprobe analyses of optically homogeneous detrital biotites from sandstones of the Visingsö Group and the Dala Sandstone, Sweden, revealed a consistently low K content (generally <0.75 atom/formula unit) and variable amounts of Fe, Mg, Al, and Si. Electron probe profiles of some biotite grains indicated two major types of interstratification, one consisting of mainly illite layers and the other apparently consisting of chlorite layers. The layer thicknesses commonly ranged between 0.5 and 3 μm. Microprobe analyses of some thick (∼5 μm) illitic layers indicated a phengitic composition, wherein the mica was relatively rich in octahederal Fe and Mg. The chloritic layers appeared to be Fe-Mg-rich and generally had octahederal totals of <6 atom/formula unit. Variations in the chemical composition of the biotite and some of the illite and chlorite were probably due to an uneven distribution of small amounts of the interstratified phases. The illite and chlorite layers were apparently formed by pseudomorphic replacement of detrital biotites, i.e., gradual replacement of one biotite layer by one layer(s) of illite and/ or chlorite during diagenesis.