113Cd solid-state nuclear magnetic resonance (NMR) was used to identify possible Cd2+ adsorption sites in montmorillonite. The montmorillonite was treated with 0.1 and 1 M CdCl2 aqueous solutions and samples with 13 and 8-µm particle size were used. The data are consistent with a two-site model for sorption of Cd2+ on montmorillonite. Cd2+ is localized in the montmorillonite in two different sites: 1) in the interlayers as hydrated Cd2+ and 2) on the external surface, probably with few H2O molecules hydrating to it. Cadmium is also adsorbed as CdCl+ in the interlayer. Treatment with a 0.1 M CdCl2 solution produces adsorption of free Cd2+ in the interlayer whereas treatment with 1 M CdCl2 resulted in adsorption of Cd2+ in both the interlayer and on surface sites and the adsorption of CdCl+ in the interlayer. A larger particle size favors Cd2+ adsorption on the external surface whereas a smaller particle size favors Cd2+ adsorption in the interlayer.

Fourier transform infrared (FTIR) spectroscopy investigations in the near infrared (N1R) region of synthetic and natural kaolinites with various octahedral substitutions have been carried out in order to elucidate the relationships between the substituted cations and specific features of the NIR spectra. The combination modes of the OH stretching and bending vibrations characterizing Fe(III), Ga(III) and Cr(III) octahedral substitutions are identified in the NIR region at 4466, 4498 and 4474 cm-1, respectively, and the first overtones of the OH stretching vibrations at 7018, 7018 and 6986 cm-1, respectively. As far as we know, the bands of kaolinites containing Ga(III) or Cr(III) have not been reported yet. For both Ga(III) and Cr(III), the NIR observations explain why the bending vibration bands of AlGaOH and AlCrOH groups are not observed in the middle infrared (MIR) region.

The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRF, Grenoble, France (λ = 0.6883, T = room temperature). The volume of the crystals was 8 and 0.8 μm3, respectively. Unit-cell parameters are: a = 5.154(9) Å, b = 8.942(4) Å, c = 7.401(10) Å, α = 91.69(9)°, β = 104.61(5)°, γ = 89.82(4)°. Space group Cl is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined also. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk ≠ 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.

Hydrothermal synthesis experiments were conducted to study the transition from smectite to corrensite. A mixture of oxides with the bulk composition of corrensite—Na0.4(Si6.4Al1.6)(Mg7.8Al1.2)-O20(OH)10—was sealed in platinum capsules with 29–37 wt. % water. One set of samples was treated in cold-seal vessels at 500°C and 2 kbar for durations of 2, 3, 6, 12, and 24 h; the other set was treated at 350°C and 2 kbar for periods of 12 to 89 d. X-ray diffraction patterns (XRD) of oriented aggregates from treated products were obtained from ethylene glycol-solvated and air-dried preparations. Samples were also heated to 350°C either in a calibrated muffle furnace, removed and quickly placed in a nitrogen filled chamber on the diffractometer, or were heated at 350°C by using a calibrated heating stage mounted on the diffractometer.

Initial mineral assemblages at both temperatures contained only saponite and serpentine. In experiments at 500°C, saponite transformed to corrensite within 6 h; in experiments at 350°C, the transformation occurred as early as 22 d. Increased experiment times at both temperatures produced increasing amounts of well-crystallized corrensite, as indicated by several well-defined XRD peaks. No evidence of a randomly interstratified chlorite-smectite (C-S) precursor to corrensite was found. The identification of pure smectite, as opposed to highly-expanded randomly interstratified C-S, was possible only when clays were dehydrated on a heating stage on the diffractometer.

These results call for a new examination of hydrothermally-altered basalt that has been reported to contain randomly interstratified C-S as an intermediate step in the reaction of smectite to corrensite or chlorite. These results also strengthen the view held by increasing numbers of investigators that corrensite should be regarded as a single phase, not as a mixed-layered phyllosilicate.

Amorphous derivates prepared by aqueous reaction of various aluminosilicate clay minerals with concentrated KF solution at 80–110°C were studied for their gas adsorption properties. The four clay minerals studied are halloysite, a well-crystallized kaolinite, a poorly crystallized kaolinite, and a montmorillonite. The gases tested are N2, O2, CH4, CO, CO2, and C2H2. The kaolin-group mineral derivatives are characterized by substantial reduction in particle size, high specific surface, and significant selectivity towards CO2 and C2H2 relative to the other gases. The montmorillonite derivative shows no increase in adsorption over the starting material, however, for all the materials high adsorption of CO2 and C2H2 was observed. Levels of gas adsorption and gas adsorption ratios are comparable to pillared clays.

Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200°C of single glasses or glass mixtures with deionized H2O or monosaline solutions (NaCl, KCl, CaCl2) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.

Development of preferred orientations of illite-smectite (I-S) has been studied using X-ray diffraction (XRD) texture goniometry to produce pole figures for clay minerals of a suite of 16 mudstone samples from a core from the Gulf Coast. Samples represent a compaction-loading environment in which the smectite-to-illite (S-I) transition occurs. In five shallow, pre-transition samples, there is no significant preferred orientation for smectite-rich I-S. Development of preferred orientation of I-S, although weak, was first detected at depths slightly less than that of the S-I transition. The degree of preferred orientation, which is always bedding-parallel, increases rather abruptly, but continuously, over a narrow interval corresponding to the onset of the S-I transition, then continues to strengthen only slightly with increasing depth. The degree of post-transition preferred orientation is also dependent on lithology, where the preferred orientation is less well-defined for quartz-rich samples.

Previously obtained transmission electron microscope (TEM) data define textures consistent with the change in orientation over many crystallites. The smectite in pre-transition rocks consists largely of anastomosing, “wavy” layers with variable orientation and whose mean orientation is parallel to bedding, but which deviate continuously from that orientation. This results in broad, poorly defined peaks in pole figures. Post-transition illite, by contrast, consists of thin, straight packets, with most individual crystallites being parallel or nearly parallel to bedding. This results in pole figures with sharply defined maxima. By analogy with development of slaty cleavage in response to tectonic stress during metamorphism, the S-I transition is marked by dissolution of smectite and neocrystallization of illite or I-S locally within the continuous “megacrystals” of smectite. The transition is inferred to have some component of mechanical rotation of coherent illite crystals within a pliant matrix of smectite. The data suggest that change in orientation and coalescence of clay packets plays an important role in the formation of the hydraulic seal required for overpressure generation.

Adsorptive-type organoclays, where hydrocarbons adsorb directly to the siloxane surfaces, were studied to find new organic cations and to determine the parameters that produce effective sorbents. Organoclays were prepared from hectorite by cation exchange with small, aromatic organic cation salt solutions. Trimefhylphenylammonium (TMPA) chloride was obtained and iodide salts of commercially-unavailable aromatic cations were synthesized and used to prepare organoclays. An aqueous mixture of benzene, toluene, ethylbenzene, and xylenes (BTEX) consistent with the composition of unleaded gasoline was used in sorption isotherms to compare the sorptive properties of the organoclays. Only the TMPA, methylphenylpyridinium (MPPyr), and trimethylammonium indan (Indan) organoclays were effective BTEX sorbents. Organoclays prepared from methylpyridinium (MPyr), trimethylammonium biphenyl (Biphenyl), and trimethylammonium fluorene (Fluorene) were poor sorbents. The MPPyr and TMPA organoclays preferentially sorbed ethylbenzene, whereas the Indan organoclay preferentially sorbed benzene and toluene. Langmuir-type sorption isotherms for the TMPA, MPPyr, and Indan organoclays implied surface adsorption, whereas linear isotherms suggested that partitioning was the sorptive mechanism for the MPyr, Biphenyl, and Fluorene organoclays. Water hydrating the small MPyr cation and the larger bulk of the Biphenyl and Fluorene cations may have blocked BTEX access to the interlayer siloxane surfaces. Although the rather bulky MPPyr and Indan cations produced effective organoclays, compact size and low hydration are organic cation properties that typically yield effective adsorptive-type organoclays.

Three samples of volcanic tuff were hydrothermally altered at ∼82°C in a soxhlet apparatus for periods from 745 to 2706 h. The samples correspond to partially altered specimens of volcanic tuff with 6 wt. % (T3a) and 9 wt. % (T3b) smectite and to the calcination product of the latter (T3c). The calcination treatment melted the smectite in the sample. Untreated samples and alteration products were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, and oxygen isotope analysis. DTA-TG of the <2-µm size fractions showed that there was a small increase of smectite relative to glass after alteration for samples T3a and T3b, with the amount of smectite increasing exponentially with time. No smectite formed in sample T3c. These results suggest that smectite acts as a nucleation site for the precipitation of new smectite. The amount of glass in the <2-µm size fraction increased, although slightly decreased relative to smectite. SEM-EDX analysis showed smectite with the approximate structural formula of Na0.22K0.08Mg0.12Ca0.03VI(Al1.47Fe0.05Mg0.48)IV(Si3.97Al0.03)O10(OH)2.

Oxygen isotope composition of the <2-µm size fraction became enriched in 18O by alteration, the >2-µm size fraction of T3b did not vary, and that of T3c was depleted in 18O. Our results are consistent with three processes during alteration: 1) oxygen isotope exchange between volcanic glass and water, 2) neoformation of smectite, and 3) hydration and consequent hydroxylation of the calcined glass.

Vermiculite from Santa Olalla, Spain, was intercalated with tetramethylphosphonium [P(CH3)4+ = TMP], using a TMP-bromide solution at 70°C for three weeks. The resulting TMP-exchanged vermiculite, which contained a small (<5% of a site) amount of residual interlayer Ca, showed near perfect three-dimensional stacking. Cell parameters are a = 5.3492(8) Å, b = 9.266(2) Å, c = 14.505(6) Å, β = 97.08(2)°, space group is C2/m, and polytype is lM. Single-crystal X-ray refinement (R = 0.052, wR = 0.061) located two crystallographically unique sites for the phosphorus atoms (TMP molecule). The phosphorus atoms are occupied partially [P1 = 0.146(6), P2 = 0.098(5)] and are offset from the central plane of the interlayer by 1.23 Å to form two P-rich planes in the interlayer. Electrostatic interactions between the P cations and basal oxygen atoms essentially balance the negative charge associated with Al for Si substitutions in the tetrahedral sites. In addition, the orientations of the TMP molecules are probably different owing to packing constraints. The H2O site is located in the center of the interlayer, at the center of the silicate ring, and ∼3.09 Å from the Ca, which is also located on the central plane of the interlayer. Other H2O molecules are present in the interlayer, but could not be located by the diffraction experiment because they are randomly positioned in the interlayer. The tetrahedral rotation angle, α, is affected by the intercalation of TMP relative to tetramethylammonium (TMA), thus indicating that 2:1 layers are not simply rigid substrates, and that dynamic interactions occur during reactions involving adsorption and exchange.

Polynuclear Al13 tridecamer species are the major hydrolyzed species of aluminum, but their occurrence in terrestrial environments has not been established. X-ray diffraction (XRD), 27Al nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) analyses show that the presence of tartaric acid (concentration range of 10−5–10−3 M), one of the commonly occurring low-molecular-weight organic acids, inhibits the formation of the Al13 tridecamer species.

In the absence of tartaric acid, the basic aluminum sulfate crystals were of tetrahedral morphology and conformed to isometric symmetry with a = 17.748 Å and space group of P4232. Increasing amounts of tartaric acid [tartaric acid/Al molar ratio (R) ranging from 0.01 to 0.05] modified the crystal morphology from the tetrahedral particles of isometric symmetry (R = 0) to rod-shaped particles of monoclinic symmetry (R = 0.01) to irregularly shaped X-ray noncrystalline microparticles (R = 0.05). Failure to detect the presence of Al13 tridecamer, the dominant hydrolyzed species of aluminum, in terrestrial environments may be partially attributed to the presence of low-molecular-weight organic acids, which inhibit the formation of Al13 tridecamer species.

This study investigates the complexes formed between amino acids, which are the natural degradation products of organic matter, and smectites. Thus, the adsorption and desorption behavior of cysteine and Na-, Ca-, Cu-homoionic smectites with different layer-charge location, a montmorillonite, and a beidellite, were studied. The clay samples were treated with Na, Ca, and Cu 1 N solutions and then with a 0.2 M cysteine solution. To test smectite-cysteine stability at acidic pH, the solids obtained were repeatedly treated with distilled water acidified to pH = 5. All treated samples were characterized by thermal, X-ray diffraction, chemical, and infrared analyses. The results showed that: 1) Na- and Ca-rich smectites adsorbed and retained small amounts of cysteine, and did not show interlayer cation-cysteine complexes, whereas the amino acid was strongly retained in the interlayer by Cu-rich smectites; 2) d(001)-values for Na- and Ca-rich smectites showed little or no expansion, whereas for the Cu-rich smectites the intercalation of the organic molecule produced a swelling of the structure; 3) the interaction mechanism of homoionic smectites with cysteine in an aqueous medium occurs by weak interactions, (e.g., van der Waals interactions, hydrogen bonding, dipole-dipole interactions, and other electrostatic forces such as entropy-driven hydrophobic bonding), and/or by complexes involving interlayer cations and organic ligands. The formation of a stable chelate complex with the saturating ion permits cysteine to be adsorbed by Cu(II)-rich smectites and to be resistant to migration in soils and groundwaters.

Adsorption and the mechanism of adsorption of the herbicide glyphosate [N-(phosphonomethyl) glycine] by hydrotalcite (HT) and by hydrotalcite calcined at 500°C (HT500) was studied. The values of the Freundlich K constant of the adsorption isotherms and the distribution coefficients, Kd, depend on the pH of the adsorption system and vary between 55.54–9603 (K) and 36.82–6252 (Kd) for HT and between 10,106–23,242 (K) and 17,801–26,558 (Kd) for HT500. X-ray diffraction and infrared spectroscopy studies showed that glyphosate is not adsorbed into the interlayer of HT. The adsorption mechanisms are (1) electrostatic attraction between the surface of HT, charged positively below pH 12 according to its point of zero charge and the glyphosate anion, and (2) ligand exchange between the P-OH and/or C=O groups of the herbicide and the Al and Mg atoms of the HT surface. The occurrence of one or both mechanisms depends on the pH of the adsorption system. These adsorption mechanisms and the amphoteric nature of glyphosate account for the variation in K and Kd values with respect to pH. Previous studies on adsorption of different organic anions by HT have only considered the mechanism of anion exchange as important.

Competitive adsorption between phosphate, tartrate and oxalate was studied on two hydroxy aluminum montmorillonite complexes (AlMt1.6 and AlMt6), which were prepared by adding a base to pH 5.5 to samples containing 1.6 and 6.0 mol Al per kg clay. The quantities of phosphate, tartrate and oxalate adsorbed were more closely related to the amount of OH-Al species coatings on the montmorillonite than to the surface area of the complexes. The adsorption capacity of phosphate was much greater than that of tartrate or oxalate for both samples. Adding molar amounts of oxalate and tartrate resulted in an oxalate/tartrate adsorption ratio (Rf) of ∼1. However, in the presence of phosphate, Rf values were <1.0, and the Rf values decreased with increasing amounts of added phosphate, indicating that tartrate competed with phosphate more effectively than oxalate. The presence of tartrate also reduced phosphate adsorption by the complexes. The efficiency of tartrate in reducing phosphate adsorption increased by increasing the initial tartrate/phosphate molar ratio and by adding tartrate 2 h before phosphate addition. Tartrate and oxalate added as a mixture in equimolar quantities were much more effective in inhibiting phosphate sorption than tartrate alone under the same organic ligand concentrations, probably because more sites with high affinity for both the organic ligands were occupied by tartrate and oxalate than by tartrate alone. The efficiency of tartrate alone, or combined with oxalate, in preventing phosphate adsorption was greater for the complex containing a lesser amount of OH-Al species coating the montmorillonite surfaces. This result may be attributable to a greater proportion of sites specific for organic ligands present on AlMt1.6 compared to AlMt6 complex.

Formation of kaolinite-smectite (K-S) mixed layers in a soil toposequence developed from basaltic parent material was examined. The soil formed in a temperate climate with alternating dry and wet seasons in Sardinia (Italy). Chemical composition and charge characteristics of the smectite component in the K-S mixed layers were analyzed to help determine a mechanism for formation. Soils were sampled at the top, intermediate, and base of a steep (35%) slope. As indicated by X-ray diffraction data, the fine clay fraction (>0.1 μm) in the soils is dominated by K-S with a decreasing proportion of kaolinite from the top (70%) to the base (30%). Rapid internal drainage induced by the slope is probably the major factor responsible for the formation of K-S. Chemical composition and charge characteristics of the smectite component in the K-S were analyzed by X-ray diffraction (intercalation with alkylammonium ions), cation exchanged capacity (CEC) and surface area measurements, and infrared spectroscopy. Results indicate that the smectite component is nearly identical over the soil toposequence. The smectite component is the same with respect to charge magnitude and chemical composition, independent of the proportion of kaolinite and smectite components. This suggests the pedogenic formation of K-S by transformation of smectite through dissolution of some smectite layers and subsequent crystallization of kaolinite between the layers of the remaining smectite crystallites.

Sorption of several organic and inorganic cations on illite (Clay Minerals Society Source Clay Imt-2) was determined experimentally and results compared to model calculations. The cations studied were crystal violet (CV+), benzyltrimethylammonium (BTMA+), benzyltriethylammonium (BTEA+), Ca2+, Mg2+, K+, Na+, Cs+, and Li+. The adsorption-model calculations involved a solution of the electrostatic Gouy-Chapman equations. The model considered specific adsorption and sorption/exclusion in the double-layer region in a closed system. Model calculations considered the simultaneous presence of four to six cations in the system. The adsorption of CV included formation of neutral and charged complexes. The adsorption attained 0.37 mol kg−1 or 150% of the cation exchange capacity (CEC) of illite in aqueous suspension. The adsorption of BTMA and BTEA did not exceed the CEC and was reduced with an increase in ionic strength. The sorption of CV below the CEC was rather insensitive to the ionic strength because of the large binding coefficients and was only slightly reduced in NaCl, CsCl, or Na2SO4 solutions. When added in amounts exceeding the CEC in high ionic strength, 0.667 M NaNO3, NaCl, or CsCl solutions, the adsorbed quantities of CV increased to three times the CEC. At high sulphate concentrations (0.333 M Na2SO4), the adsorption was below the CEC. Model calculations yielded satisfactory simulations for the adsorption, particularly for cations added in amounts approaching or exceeding the CEC. The binding coefficients for formation of neutral complexes followed the sequence: CV > Ca > BTMA > BTEA > Cs > Mg > K > Na > Li. Model calculations also suggested that sites were present which bound exchangeable cations, particularly K+, Na+, and Mg2+, very tightly.

Synthetic hematites prepared in the presence of phosphate can incorporate phosphorus (P) in forms other than phosphate adsorbed by ligand-exchange on the crystal surface. To investigate the nature of such occluded P, which is also found in some natural specimens, we prepared 13 hematites by aging ferrihydrite precipitated from Fe(NO3)3-KH2PO4 solutions. The P/Fe atomic ratio of the resulting hematites ranged from 0 to 3% and all incorporated significant amounts of OH. As P content is raised, particle morphology changes from rhombohedral to spindle or ellipsoid-shaped. Despite the grainy appearance in transmission electron microscope images, X-ray diffraction data indicate that the particles are single crystals. Specific surface area ranged from 66 to 91 m2g−1, partly in micropores. The intensity of the absorption bands due to Fe3+ ligand field transition in the visible region, as measured by the second derivative of the Kubelka-Munk function, suggests that both OH and P contribute to an Fe deficiency in the structure. Such a deficiency is also apparent from the 104/113 peak intensity ratio in the X-ray diffraction patterns. The c unit-cell length increases with increasing P content. The infrared spectra exhibit four bands in the P-OH stretching region (viz., at 936, 971, 1005, and 1037 cm−1) which suggest that occluded PO4 possesses a low symmetry. Congruent dissolution of P and Fe was observed on acid treatment of the hematites, the dissolution rate being negatively correlated with the P content. All observations are consistent with the occluded P in the hematites being structural. A model is proposed where P occupies tetrahedral sites in the hematite structure, thus resulting in an Fe deficiency and facilitating proton incorporation.

Transmission electron microscopy (TEM) observation shows narrow regions in a Ti-containing Mg-rich annite of composition (K0.90Na0.02)(Mg0.72Fe2+1.78Mn0.03Ti0.27Al0.05)(Si2.77Al1.23)O10(OH,F)2 from a granitic rock, where the ±60° and 180° stacking angles occur extensively. These regions are a few hundreds of nanometers thick along the [001]* direction and are within 1M or 2M1 annite. The stacking sequence in one of these regions was determined by two atomic-resolution images recorded along [1̄10] and [010] of the same crystal. Stacking sequences with ± 120° or 180° rotations are dominant, although those with ±60° rotations occur also. Locally 2O and more complex sequences exist. Compositional analysis by TEM indicated no difference in the chemical compositions between these regions and the adjacent ones with regular 1M or 2M1 stacking sequence. The origin of these unusual stacking sequences in annite is discussed.