Wyoming montmorillonite, <2-µm particle size, saturated with Na, K, Mg, Ca, and Ba ions, was reacted with uranyl nitrate solutions in the concentration range 1–300 ppm uranium. With constant amounts of clay and solution volume, the adsorption isotherms of uranyl ions on the clay followed Langmuir-type curves with increasing concentration of uranium. The maximum adsorption derived from linear Langmuir plots corresponds to the exchange capacity of the clay. Experiments with solutions of constant volume and constant ionicity, but with variable proportions of uranyl and other cations, showed that uranyl ions were strongly preferred by the clay to Na+ and K+, but less strongly than Mg2+, Ca2+, and Ba2+.

Chemical analyses of uranyl montmorillonites prepared with nitrate solutions, 0.05 M and pH ≃ 2.0, gave interlayer cations (UO2)0,094H0,12. Addition of NaOH to the uranyl nitrate solution to increase the pH to 4.0 gave a montmorillonite with interlayer cations (UO2)0,083Na0,12H0,04. A fully exchanged uranyl montmorillonite was prepared with 0.05 M uranyl acetate solution, pH ∼ 4.0, followed by further treatment with 1.25 × 10−5 M solution, pH ∼ 4.5. The resulting interlayer composition was (UO2)0,19(H2O)1.15 which corresponds with the hexahydrate ion, [(UO2)−6H2O]. X-ray powder diffraction and thermal data are recorded for the fully exchanged uranyl montmorillonite.

The rehydration properties and behavior of interlayer cations of Ca-, Mg-, Na-, and K-saturated homoionic saponite and vermiculite heated at various temperatures were examined and their rehydration mechanisms elucidated. The most notable features of saponite were (1) except for the Mg-saturated specimen, all saponite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: K+ > Na+ > Ca2+ > Mg2+; (3) the interlayer cations apparently migrated into hexagonal holes of the SiO4 network on thermal dehydration; and (4) the b-parameter expanded on thermal dehydration. The rehydration properties and behavior of interlayer cations of vermiculite were: (1) except for the K-saturated specimen, all vermiculite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: Mg2+ > Ca2+ > Na+ > K+; (3) the interlayer cations apparently did not migrate into the hexagonal holes, but remained at the center of the interlayer space, even after thermal dehydration; and (4) except for the K-saturated specimen, the 6-parameters of the samples contracted on thermal dehydration. The different rehydration properties of saponite and vermiculite were apparently due to the behavior of the interlayer cations during thermal dehydration. For rehydration to occur, the interlayer cations of saponite had to migrate out of the hexagonal holes. Consequently, saponite saturated with a large cation rehydrated rapidly, whereas saponite saturated with a small cation rehydrated slowly. On the other hand, the interlayer cations of vermiculite remained in the interlayer space; therefore, the rehydration properties of vermiculite were strongly affected by the hydration energies of the interlayer cations. Furthermore, electron diffraction patterns suggested that the saponite and vermiculite consisted of random stacking and ordered stacking of adjacent 2:1 layers, respectively. The nature of the stacking of the minerals seemed to be the most important factor controlling the behavior of interlayer cations in the thermal dehydration process.

Analytical, spectroscopic, and X-ray powder diffraction techniques were used to investigate the adsorption of the herbicide sodium acifluorfen (acifluorfen = 5-[2-chloro-4-(trifluorornethyl)phenoxy]-2-nitrobenzoic acid) from aqueous solution onto Cu2+-, Al3+-, Fe3+-, and Ca2+-saturated montmorillonite. As indicated by infrared and electron spin resonance spectra, which are coincident with those of the corresponding solid metal complexes, and by the basal spacings, which are the same for all the samples, acifluorfen extracted the exchangeable ions from the clay interlayer and precipitated them on external surfaces. The process involved the replacement of sodium as the saturating ion and was due to the formation of insoluble complexes between the herbicide and polyvalent metal ions.

The effect of ethylene oxide-sterilization on homoionic (Na+, K+, Ca2+, Cu2+, Al3+, and Fe3+) montmorillonite samples was examined. The results indicate that ethylene oxide polymerized to polyethylene glycol in the interlayer of Cu2+-, Al3+-, and Fe3+-saturated clays, as substantiated by the increase in the d(001) values, as well as by the decrease in the cation-exchange capacity after reaction. On the contrary, ethylene oxide failed to react in the presence of the Na+-, K+-, and Ca2+-clays, likely due to the lower acidity of the exchange cations.

The adsorption of the pesticide Fluazifop, (RS)-2-[4-[[(5-trinuoromethyl)-2-pyridin-yl]oxy]phenoxy] propanoic acid, on homoionic Cu2+-, Fe3+-, and Al-bentonites was investigated by infrared and electron spin resonance spectroscopy. For comparison, the binary complexes of the acid containing the above ions were prepared and characterized. On the whole, the results show that the interaction of the acid with the clay may have involved both the protonation of the pyridine nitrogen atom, due to a proton transfer from the acid metal-bound water, and the formation of direct bonds between the carboxylate groups and the exchange cations. The extent of these interactions was dependent on the nature of the metal ions, the Cu ions being more effective in producing CHCl3-extractable neutral carboxylate complexes, while Al and Fe favored the formation of species bearing protonated nitrogen atoms and un-dissociated carboxyl groups.

The adsorption from chloroform solution of the herbicide diclofop, (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid, and its methyl ester diclofop-methyl on Cu2+-, Al3+-, and Fe3+-exchanged bentonite samples was investigated. For comparison, the complexes formed by diclofop were synthesized and studied. Diclofop adsorbed on the clays and formed carboxylate bonds to the interlayer ions. Diclofop-methyl also adsorbed, but its interaction involved the formation of hydrogen bonds with water molecules in the interlayer. Traces of diclofop were observed in both the solution and the clays after adsorption of diclofop-methyl, indicating that some hydrolysis of the ester to the corresponding acid occurred. Thus, pesticides forming neutral complexes with interlayer cations in montmorillonite in soils may be extractable by solvents and therefore released into the environment.

The crystal structure of bannisterite, a modulated, mica-like mineral species, of general composition Ca0.5(K,Na)0.5(Mn,Fe,Mg,Zn)10(Si,Al)16O38(OH)8·nH2O, has been solved and refined for specimens from Franklin Furnace, New Jersey (FF), and Broken Hill, Australia (BH). The crystals are mono-clinic in space group A2/a, with (for FF) a = 22.265(1) Å, b = 16.368(1) Å, c = 24.668(2) Å, β = 94.285(5)°; and (for BH) a = 22.286(1) Å, b = 16.386(1) Å, c = 24.575(2) Å, β = 94.355(7)°; Z = 8. Refinement with anisotropic thermal factors reached Rw = 0.034 (FF) and 0.039 (BH). Like stilpnomelane and ganophyllite, bannisterite has a modified 2:1 trioctahedral layer structure in which some of the tetrahedra are inverted towards the interlayer region and linked to inverted tetrahedra in the opposite layer. The octahedral sheet is strongly corrugated along b. The tetrahedral sheet consists of 5-, 6-, and 7-fold rings, and bond distance calculations indicate that Al is concentrated into two of the four inverted tetrahedra. The interlayer Ca, K, and H2O species are highly disordered, as indicated by anomalously large temperature factors and partial occupancies. Localized differences in the Al/Si arrangements in the inverted tetrahedra induce disorder among the interlayer cations.

The compositions, fabrics and structures of authigenic minerals that formed recently from silicic volcanic ash layers from a 1300-meter sediment column obtained at ODP Site 808 of the Nankai Trough were studied using XRD, STEM, AEM and SEM. Smectite and zeolites were first detected as alteration products of volcanic glass with increasing depth, as follows: smectite at 200 m below seafloor (mbsf) (20 °C), clinoptilolite at 640 mbsf (60 °C) and analcime at 810 mbsf (75 °C).

A primitive clay precursor to smectite was observed as a direct alteration product of glass at 366 mbsf (approximately 30 °C). High defect smectite with lattice fringe spacings of 12 to 17 Å and having a cellular texture filling pore space between altering glass shards occurs at 630 mbsf. Packets of smectite become larger and less disordered with increasing depth and temperature. The smectite that forms as a direct alteration product of volcanic glass has K as the dominant interlayer cation.

With increasing depth, smectite becomes depleted in K as the proportion of clinoptilolite increases, and then becomes depleted in Na as the proportion of analcime increases. The composition of the exchangeable interlayer of smectite appears to be controlled by the formation first of K-rich clinoptilolite and then Na-rich analcime, via the pore fluid, giving rise at depth to Ca-rich smectite. Smectite reacted to form illite in the interbedded shales but not in the bentonites. Paucity of K in smectite and pore fluids, due to formation of clinoptilolite under closed system conditions, is believed to have inhibited the reaction relative to shales.

The adsorption of the herbicide imazamethabenz-methyl, a mixture of the two isomers methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidazol-2-yl]-4-methylbenzoate para isomer) and methyl (±)-2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-1 H-imidazol-2-yl]-5-methyl-benzoate (meta isomer), from water onto Al3+, Fe3+-, Ca2+-, K+- and Na+-montmorillonite was studied by analytical (HPLQ methods. The adsorption from an organic solvent was also investigated by spectroscopic (IR) and X-ray diffraction measurements. It was observed that, depending on the acidic properties of the exchangeable cations, two different mechanisms may take place. The first one, acting on Fe3+- and Al3+-clays, involves the protonation of the more basic nitrogen atom of imidazolinone ring of the herbicide because of a proton transfer from the acidic metal-bound water, followed by adsorption on the clay surfaces. In this case, the clay surfaces have greater affinity for the meta than the para isomer, due to the extra-stabilization of the meta protonated form by resonance. The second mechanism, taking place on Ca2+-, K+- and Na+-clays, is hydrogen-bond formation between the ester carbonyl group of the herbicide and hydration water metal ions and is not affected by the structure of the isomers.

The adsorption of the herbicide dimepiperate S-(α;α-dimethylbenzyl)-1-piperidinecarbothioate on homoionic Fe3+-, Al3+-, Ca2+-, and Na+-montmorillonite was studied in aqueous medium. The adsorption is described well by the Freundlich equation. The adsorption capacity decreases in the order Fe3+ > Al3+ > Ca2+ > Na+ clay. The dimepiperate adsorption from chloroform solution was also investigated by analytical, spectroscopic, and X-ray powder diffraction techniques. IR results suggest that the adsorption involves the interaction of the thioester carbonyl group of dimepiperate possibly with the surrounding water of metal ions. On Al3+ and Fe3+ clays, this interaction leads to hydrolysis of the thioester bond and formation of the thiol and carbamic acid derivatives that yield α-methylstyrene and piperidine, respectively.

Acid-activated clays are inexpensive materials that are used extensively in the removal of unsaturated compounds on an industrial scale. The performance of bentonitic clays in removing these compounds relies heavily on the types of raw clays and acids used in the activation process. In this work, we report on the removal of olefins from aromatic streams by bentonitic clays activated via two different routes. After preliminary tests of four different natural clays, the best clay was selected in terms of it having high swelling index, cation-exchange capacity, specific surface area and suspension stability values. Activation was achieved with hydrochloric acid (HCl) and sulfuric acid (H2SO4), and olefin removal was evaluated after holistic clay characterization by means of X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller (BET) specific surface area analysis, ζ-potential analysis, Fourier-transform infrared (FTIR) spectroscopy after treatment with pyridine, scanning electron microscopy and transmission electron microscopy. The increased basal spacing, replacement of H+ with interlayer cations and retained structural stability of the clay after acid treatment contributed to the improvement of olefin removal for HCl-activated clay. The HCl-activated clay was more efficient in terms of olefin removal than its H2SO4-activated counterpart, removing up to 90% of olefin components after 40 h. Based on pyridine-FTIR spectra and quantitative measurement of the acidic properties of the samples, HCl treatment increased the total number acid sites (Brønsted and Lewis) by approximately ninefold compared to the pristine natural clay and by approximately fourfold compared to the H2SO4-activated clay.

The low-charge dioctahedral 2:1 phyllosilicates are an important group of clay minerals that have a low degree of cation substitution and very weak interlayer interatomic interactions which are difficult to reproduce with quantum mechanical calculations. In order to study the crystallographic properties of these compounds with density functional theory (DFT) quantum-mechanical methods, an optimization of norm-conserving pseudopotentials of Al, Si, O, H and Na atoms has been carried out, and an optimization of the cutoff radii of the basis sets has been accomplished. Crystallographic properties and vibrational stretching frequencies of the OH groups, ν(OH), have been calculated, being consistent with previous computational and experimental results. All frequencies can be related to the different molecular environment of the OH groups. The effect of octahedral Fe3+ substitution on the ν(OH) frequency is reproduced. Several configurations of cation substitutions and interlayer cation (IC) positions are studied in low-charge dioctahedral 2:1 phyllosilicates, such as Al4(Si7–xAlx)O20(OH)4Nax, with x = 0.25, 0.50 and 0.75, indicating that the IVAl3+ is highly dispersed and the IC tends to be in the substituted ditrigonal hole. For the Al4(Si7Al)O20(OH)4Na composition, the trans-vacant form is more stable than the cis-vacant one.