A study was undertaken to investigate the adsorption of hemin, protoporphyrin and hematoporphyrin by kaolinite and a Ca-montmorillonite in aqueous solutions buffered at pH 4 and 9.

Although experimental restrictions at pH 4 prevented the complete characterization of the adsorption isotherms, kaolinite did exhibit a saturation of exchange sites by the cationic porphyrins. Both kaolinite and montmorillonite displayed a similar saturation of sites by the porphyrins in their anionic forms at pH 9. The major differences in the adsorption isotherms are attributed to differences in the exchange capacities of the clays.

Adsorption of the porphyrins at pH 9 was inhibited largely by phosphate treatment of the clays; this effect is interpreted as blockage of the anion exchange sites by irreversibly-bound phosphate.

A number of smectitic samples from Almeria (SE Spain) were studied by chemical analysis, DTA, TG, XRD (oriented aggregates with ethylene glycol treatment and Greene-Kelly test), FTIR and MAS NMR. Chemically they resembled a beidellite-montmorillonite series, displaying DTA/TG characteristics already quoted in the literature in beidellite descriptions. They did not swell after the Greene-Kelly test, as it has also been reported for some beidellites. Nevertheless XRD of the oriented, glycolated samples, FTIR, MAS NMR and revision of the chemical analysis demonstrated that they were mixed-layered kaolinite/montmorillonite. It is possible that some of the reported beidellites in the literature are kaolinite/montmorillonite. Beidellite characterization must be supported by several different techniques.

OH-Cr smectites were prepared with different mmol Cr/g smectite: 0.5, 1.5, 3.5, 5, 10 and 20 by treatment with hydroxy-chromium solution prepared at 60°C and one day of hydrolysis with OH/Cr = 2. The samples were characterized by X-ray diffraction (XRD), differential thermal analyses (DTA) and N2 adsorption-desorption isotherms.

The d(001) spacings of OH-Cr-smectite were different according to Cr added/g smectite. Larger d(001) spacings: 1.95, 2.05 and 2.07 nm were obtained with 5, 10 and 20 mmol Cr per gram of sample. DTA diagrams of smectite treated with OH-Cr solution showed exothermic peak at 420°C corresponding to Cr203 (confirmed by XRD). N2 adsorption-desorption isotherms of smectite treated with different amounts of Cr preserved the same slit-shaped pores than original sample, but with different micropore volume. This behavior was maintained until treatment temperature of 380°C. The specific area of smectite was increased from 36 to 175 m2/g after treatment with OH-Cr solution. The textural characteristics of OH- Cr smectite heated up to 420°C were changed. The specific area decreased and mesopore volume was produced. The different Cr added modified the structural and textural behavior.

Nano-ball allophane is a hydrous Al silicate with a hollow-sphere morphology that contains some defects or pores along the spherule walls. Enlargement of the pore openings by dilute alkali treatment was confirmed by cation exchange capacity determinations using various alkylammonium cations as replacement cations. An allophane sample with a low Si/Al ratio (0.67) was equilibrated with 10 mM CaCl2 (pH = 6.0) and the Ca2+ retained was extracted using aqueous 1 M NH4C1 or alkylammonium chloride salts. The Ca2+ extracted by ${\text{NH}}_4^{+}$ was 15.1 cmolc kg−1, but ${\text{CH}}_3{\text{NH}}_3^{+}$${\rm{C}}{{\rm{H}}_3}{\rm{NH}}_3^ + $ (mean diameter = 0.38 nm) only extracted 7.9 cmolc kg−1 of Ca2+. After 10 mM NaOH treatment (0.25 g:100 mL) of the allophane, the Ca2+ extracted by ${\text{NH}}_4^{+}$${\rm{NH}}_4^ + $ was 29.7 cmolc kg−1, 29.6 cmolc kg−1 by ${\text{CH}}_3{\text{NH}}_3^{+}$${\rm{C}}{{\rm{H}}_3}{\rm{NH}}_3^ + $, and 29.4 cmolc kg−1 by ${{\text{(CH}}_3\text{)}}_2{\text{NH}}_2^{+}$${{\rm{(C}}{{\rm{H}}_3}{\rm{)}}_2}{\rm{NH}}_2^ + $. The extraction of Ca2+ by the large ${\text{C}}_2{\text{H}}_5{\text{NH}}_3^{+}$${{\rm{C}}_2}{{\rm{H}}_5}{\rm{NH}}_3^ + $ cation (mean diameter = 0.46 nm) only decreased to 26.1 cmolc kg−1, indicating that pore diameters were enlarged from ∼0.35 to 0.45 nm. The significant increase in Ca2+ retention after NaOH treatment was attributed to the dissociation of increased numbers of newly exposed silanol groups in the enlarged pores. The low Si/Al ratio of the NaOH-dissolved material (0.35) and the decreased intensity of the 348 cm−1 IR band also suggested selective dissolution of the pore region. For allophane with a high Si/Al ratio (0.99) and much accessory polymeric Si, dissolution of polymeric Si and of the pore region occurred simultaneously. Alkali treatment produced a smaller increase in pore size and Ca2+ retention for allophanes with large Si/Al ratios than for allophanes with small Si/Al ratios. It was concluded that by altering the dilute alkali treatment conditions and varying the Si/Al ratio of allophane, the extent of structural modification or pore enlargement of the hollow spheres might be controlled.

The deintercalation of a low-defect kaolinite intercalated with hydrazine was studied by X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), and Raman microscopy over 30 d. X-ray diffraction showed that the kaolinite was fully intercalated. More than 120 h were required for the hydrazine-intercalate to decompose. The Raman spectra of the hydrazine intercalate showed only a single band at 3620 cm−1, which was attributed to the innerhydroxyl group. Upon deintercalation, additional Raman bands were observed at 3626 and 3613 cm−1. These bands decreased in intensity with further deintercalation. As deintercalation proceeded, the bands assigned to the inner-surface hydroxyl groups at 3695, 3682, 3670, and 3650 cm−1 occurred and increased in intensity. DRIFT spectra showed two bands at 3620 and 3626 cm−1 for the fully intercalated kaolinite only. Upon deintercalation, an additional band assigned to intercalated water was observed at 3599 cm−1 and increased in intensity at the expense of the 3626-cm−1 band. Bands attributed to the innersurface hydroxyl groups increased in intensity with deintercalation. Both the Raman and DRIFT spectra showed complexity in the NH-stretching region with two sets of NH-symmetric and antisymmetric stretching bands. Deintercalation was followed by the loss of intensity of these bands. Significant changes were also observed in the hydroxyl deformation and water-bending modes as a result of deintercalation. A model of hydrazine intercalation of kaolinite based on the insertion of a hydrazine-water unit is proposed. The hydrated end of the hydrazine molecule hydrogen bonds with the innersurface hydroxyl groups resulting in the formation of a band at 3626 cm−1 in the DRIFT spectra.

A high-pressure, high-temperature cell was used to monitor the basal X-ray powder diffraction spacing of Na-saturated Cheto montmorillonite in contact with NaCl solutions at temperatures as high as 200°C and hydraulic pressures as high as 6700 psi (456 bar). The 003 and 005 reflections were used to determine d(001) of the smectite. The montmorillonite, in 1 molal NaCl, exhibited a d(001) of 15.4 Å at room temperature and pressure and a d(001) of 15.6–15.7 Å under 500–2200 psi hydraulic pressure. The basal spacing of the clay in 5 molal NaCl was 15.2 Å and 15.33–15.45 Å at 1 bar and 750–6700 psi (53–456 bar), respectively. Because no changes in the basal spacing with increasing temperature to 200°C were detected in any of the experiments, this Na-smectite probably exists as a two-water-layer complex under diagenetic conditions.

The alteration of spodumene to cookeite has been identified in a Li-bearing aplite-pegmatite from northern Portugal. Optical microscopy and scanning and transmission electron microscopy (SEM/TEM) were used to characterize the alteration products in both cookeite + quartz and cookeite + kaolinite ± mica assemblages. Mutual relationships between the minerals were assessed using back-scattered electron imaging. The first assemblage occurs along the cleavage planes of spodumene, whereas the second forms as the result of spodumene breakdown. Fine mica grains surrounded the cookeite aggregates in the second assemblage only. Precipitations of cookeite and quartz in open pore spaces and parallel packets of cookeite and kaolinite were identified by TEM. Selected area electron diffraction carried out on cookeite identified a layer-stacking sequence from highly disordered to one-layer order-disorder with a lesser participation of two-layer polytypes. The thickness of one-layer cookeite packets averaged ∼85 −100 nm. Disordered cookeite has a mean thickness of 450 nm. The chemistry of cookeite was analyzed by both electron and ionmicroprobe techniques. The structural formula of cookeite from the first assemblage corresponds to: Al2.0(Si3.23Al0.766)O10(OH)2(Al1.80Li1.166Mg0.004Fe0.09)(OH)6. Two distinct compositional varieties were found: one corresponding to ideal cookeite, whereas the second belongs to the cookeite-donbassite join.

The thermodynamic stability field for the observed minerals was calculated using the SUPCRT® programme. Two distinct stages of cookeite crystallization are discussed. The lower pressure and temperature stability of the reaction of spodumene to cookeite + quartz were estimated at ∼2.4 kbar and 240°C. The cookeite + kaolinite ± mica assemblage is still in equilibrium with quartz at ∼2.2 kbar and 220°C. The lower limit for the stability of cookeite was found at 205°C and 2 kbar.

To assign far infrared (FIR) absorption bands of K+ in muscovite, dichroic experiments were performed. For a muscovite crystal rotated about a crystallographic axis, c*, a, or b, two bands corresponding to vibration modes of K+ appear, respectively, at 107 and 110 cm−1 (rotation about c*), 107 and 143 cm−1 (rotation about a), and 110 and 143 cm−1 (rotation about b). Two in-plane modes at 107 and 110 cm−1 and one out-of-plane mode at 143 cm−1 are identified for the vibrations of K+ in muscovite. Each of these transition moments are near the crystallographic axes b, a, and c, respectively. These observations match well predictions based on the approximate C3i symmetric environment of K+, although the site symmetry in the space group of muscovite is only C2.

New and published experimental data on hydrothermally treated (2-kbar water pressure, 300–400°C natural clay minerals is used to construct phase diagrams in composition and pressure-temperature space which define the phase relations of mixed layering solid solution in dioctahedral (illite-montmorillonite) and trioctahedral expanding chlorite and corrensite-like minerals. Three major relations are established:

1. (1) The R3+, i.e. Al13+ and/or Fe3+, content of the assemblage will control whether or not an expanding chlorite or corrensite phase will appear. These minerals are R3+-rich in composition as well as R2+ (Mg and Fe2+)-rich.

2. (2) Temperature-pressure variables control the type and composition of the mixed layered illite-montmorillonite mineral which is stable with aluminous phases. A sequence of different types of mixed layered ordering can be established which might be correlated with diagenetic or epimetamorphic grade.

3. (3) The presence of ‘metamorphic’ trioctahedral phyllosilicate phases, i.e. those due to the effects of earliest metamorphism, is correlated with the P-T-X variables. These phases include 7 Å chlorite (iron-rich), 14 Å chlorite and the expanding chlorite and corrensite-like minerals.

It is not possible to give absolute temperatures for the different reactions implied by the phase diagram due to the slow rate of crystallization in the experiments. However, the general sequence of assemblages and the phase relations proposed should correspond to those which are encountered in nature when pressure and temperature vary.

Infrared (Visible-Near Infrared-Shortwave Infrared (VNIR-SWIR)) spectroscopy is a cost-effective technique for mineral identification in the field. Modern hand-held spectrometers are equipped with on-board spectral libraries that enable rapid, qualitative analysis of most minerals and facilitate recognition of key alteration minerals for exploration. Spectral libraries can be general or customized for specific mineral deposit environments. To this end, careful collection of spectra in a controlled environment on pure specimens of key minerals was completed using the National Mineral Reference Collection (NMC) of the Geological Survey of Canada. The spectra collected from specimens in the ‘Kodama Clay Collection’ were processed using spectral plotting software and each new example was validated before being added to a group of spectra considered for incorporation into the on-board library of the handheld ASD-TerraSpec Halo near-infrared (NIR) mineral identification instrument. Spectra from an additional suite of mineral samples of the NMC containing REE, U, Th, and/or Nb are being prepared for a new, publicly available spectral library. These minerals commonly occur in carbonatite or alkali intrusive deposits, and as such will assist in the exploration for critical metals.

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 dehydration and migration of the interlayer cation of the synthetic beidellite Na0.7Al4.7Si7.3O20-(OH)4·nH2O, were studied with solid-state 23Na and 27Al MAS-NMR, heating stage XRD, and thermogravimetric analyses (TGA, DTA). The 23Na MAS-NMR of Na-beidellite at 25°C displays a chemical shift of 0.2 ppm, which indicates a configuration comparable with that of Na+ in solution. Total dehydration proceeds reversibly in two temperature ranges. Four water molecules per Na+ are gradually removed from 25° to 85°C. As a result, the basal spacing decreases from 12.54 Å to 9.98 Å and the Na+ surrounded by the two remaining water molecules is relocated in the hexagonal cavities of the tetrahedral sheet. The chemical shift of 1.5 ppm exhibited after the first dehydration stage illustrates the increased influence of the tetrahedral sheet. The high local symmetry is maintained throughout the entire first dehydration stage. During the second dehydration, which proceeds in a narrow temperature range around 400°C, the remaining two water molecules are removed reversibly without any change of the basal spacing.

Clay-rich deposits of Upper Cretaceous levels in the Taveiro (Reveles and S. Pedro) and Aveiro (Bustos) regions of west-central Portugal are economically and environmentally important, but detailed chemical and mineralogical characterization is lacking. The purpose of this study was to partially fill that gap by correlating the trace-element geochemistry (particularly the rare earth elements, REE) with the mineralogy of both the whole rock and of the <2 μm fraction along selected stratigraphic levels of the formations. The results will help the ceramics industry in the region and will be important in paleoreconstruction environmental studies.

Mineralogical and chemical characterizations were carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), and instrumental neutron activation analysis (INAA). The following clay-mineral associations were identified: (1) at Reveles — smectite, illite, and kaolin minerals; (2) at S. Pedro — kaolin minerals and illite; and (3) at Bustos — illite, kaolin minerals, and mixed-layer illite-smectite. The distribution of trace elements in the <2 μm fraction depended on the clay mineralogy, suggesting that the trace elements were incorporated in, adsorbed to, or even replaced major elements in the clays, as follows: (1) first-row transition elements, particularly Zn and Ga, were enriched when smectite predominated; (2) As, Rb, and Cs were enriched in this fraction of the S. Pedro deposit, the only one with Fe (oxyhydr)oxides and a high proportion of illite; and (3) REE were more concentrated when kaolin minerals predominated. Eu was enriched in the <2 μm fraction, which was due to preferential incorporation in the Fe (oxyhydr)oxides and/or carbonates.

IronIII for TiIV substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. Mössbauer- and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated FeIII in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm−1, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H2O/mol Fe. At 600°C structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiO5, was formed.

Spray drying dilute suspensions of bentonitic montmorillonite produces a powder that shows totally random orientation of the crystallites within a sample large enough to diffract X-rays. The powder is collected by an electrostatic precipitator and can be handled in the normal mounting processes without introducing preferred orientation. Electron micrographs show this powder to be composed on a small scale of thin, crumpled, and rolled films. The extremely small montmorillonite crystallites that make up the film are oriented with [001] directions perpendicular to the film surface. Orientation within the plane of the film is random as shown by selected area electron diffraction. Crumpling and rolling of the film is sufficient to make the orientation of [001] directions random in three dimensions in a large sample when X-ray diffraction is registered.

The X-ray diffraction patterns all show diffraction maxima (both hk and 00l), and their relative intensities with respect to each other can be determined. The line broadening of the 06 and the 003 peaks was studied. The average crystallite size as calculated from the line broadening varied from six to eleven unit layers thick for four bentonitic montmorillonites. The average lateral dimension of crystallites varied from 140 Å to 250 Å. Ratios of lateral dimensions to thickness varied from 2.3 to 3.4.

Selected chemical and diffraction analyses from the literature, supplemented by thermal and thermogravimetric analyses and infrared absorption observations, are utilized to construct a rational model of the water arrangement in natural vermiculites.

A super cell is arranged by simple modification of the Hendricks water nets to accommodate the somewhat higher water contents, indicated by weight loss analyses, and the exchangeable cations.

A three-cell unit (15.6 × 9 Å) contains two Mg2+·6H2O octahedra centered at the corners and face centers and four 4H2O squares centered about ±5.2 Å along a between the octahedra. The arrangement affords twenty hydrogen bonds near 2.75 Å, twelve between silicate and water layers and eight between water layers, and thirty-two hydrogen bonds near 3.0 Å within water layers. The remaining four hydrogens are not active in the bonding system. The environment of each water molecule is a distorted tetrahedron.

A broad infrared absorption band shows maxima at about 3600, 3450 and 3350 cm−1 at normal incidence, with increased activity in the highest and lowest energies when a flake is tilted. It is concluded that OH axes in the shortest bonds are more inclined to the cleavage planes than are the intermediate length axes.

Halloysite was mechanically ground in the presence of NaCl, KCl, RbCl, RbCl and CsCl, and i.r. spectra were recorded after various periods of grinding, up to 10 min. Changes in the wave-numbers and sharpness of absorption bands were interpreted using assignments accepted for kaolinite. Diminution of absorption bands of OH groups and the appearance of new bands indicate formation of complexes of halloysite with KCl, KBr, RbCl, and CsCl. Water was essential in the complex formation, which may be formulated:

The amount of the complex formed depended on the salt and the time of grinding. Complex formation requires that the cation be large enough to serve as a “structure breaker” of the interlayer water sheet. Complex formation also requires that the cation be a weak electron acceptor. Grinding also led to changes in the fine structure of the tactoid.

The possibility of using the i.r. spectrum of halloysite as a finger print for identification of the mineral is discussed. It was concluded that NaCl is the most reliable dispersing agent to determine whether or not a mineral sample belongs to the kaolinite group. Disks in RbCl may be used to differentiate between kaolinite and hydrated halloysite.