Interlayer sodium ions of montmorillonite were exchanged with hydroxy-bismuth polycations which were prepared from bismuth perchlorate solutions by the addition of NaOH. Assuming the charge density of the silicate layer to be unchanged, the compositions of the polycations involved in the exchange can be estimated from the amount of bismuth taken up by the montmorillonite and from the ignition loss between 110° and 800°C. The derived compositions are near [Bi6(OH)16]2+ irrespective of the ratio of OH:Bi in the perchlorate solution. The basal spacing of the hydroxy-bismuth montmorillonites is about 16 Å at 110°C, which corresponds to that of hydroxy-chromium montmorillonite having a high surface area of about 250 m2/g. The surface areas of the hydroxy-bismuth montmorillonites, however, are less than 80 m2/g.

Silica-intercalated hectorite with an 001 spacing of 12.6 Å and a N2 BET surface area of 220 m2/ g was prepared by hydrolysis and oxidation at 500°C of hectorite containing a silicon acetylacetonate complex. The intercalate swelled to higher spacings upon adsorption of water, glycerol, and pyridine, but the silica was not expelled when the interlayers swelled and contracted in successive adsorption/desorption cycles. The surface area measured by isobutane adsorption agrees with the N2BET surface area, suggesting that the interlayers are available for adsorption of aliphatic hydrocarbons. The intercalated silica did not inhibit the ability of the interlayers to enter into cation-exchange reactions, as judged from Cu2+-binding experiments. Infrared studies of NH3-, pyridine-, and NO2-adsorption indicate the presence of Bronsted acidity and the absence of Lewis acidity in the interlayer regions.

The pillaring of Na-montmorillonite with cationic oligomers of hydroxyaluminum (COHA) in the presence of an aqueous solution of polyvinyl alcohol resulted in the formation of a clay having a large surface area and pore volume. The pore-size distribution determined from a N2 adsorption/desorption hysteresis was narrow and centered at about 25 Å. The peak width at half height in the distribution curve was < 5 Å. As a result of delamination, the layer structure of the prepared clay was found from X-ray powder diffraction measurements to be lost. Short-range ordering, however, still existed in this delaminated clay, because exchangeable cations in the montmorillonite completely exchanged with Al3+, a requisite step for pillaring.

The order of adding the starting materials (Na-montmorillonite, polyvinyl alcohol, and COHA) greatly affected the surface area and the pore volume of the delaminated clay. Two orders of addition (Namontmorillonite, then COHA, then polyvinyl alcohol; and COHA, then Na-montmorillonite, then polyvinyl alcohol) gave no measurable surface area and pore volume. Two other orders of addition (polyvinyl alcohol, then COHA, then Na-montmorillonite; and polyvinyl alcohol, then Na-montmorillonite, then COHA) gave surface areas of 107 and 160 m2/g and pore volumes of 0.13 and 0.29 cm3/g, respectively. The amounts of the COHA solution and polyvinyl alcohol added greatly influenced the surface area and pore volume of the delaminated clay. Both properties increased monotonically with increasing amount of added polyvinyl alcohol, and increased to a maximum and then decreased with increasing amount of added COHA solution. The maximum surface area of the prepared delaminated clay was 330 m2/g.

Interaction of La3+- and Ce3+-exchanged hectorites with oligomeric hydroxy-Al cations results in the formation of cross-linked hectorites possessing moderately high surface areas (~ 220–280 m2/g) and high thermal stability. The basal spacings of these products were generally in the range 17.0–18.0 A, the exact d(001) value depending on the age of the hydroxy-Al oligomeric solution and on the pH of the starting hectorite dispersion. Interaction of Li- or Ce-fluorhectorite with hydroxy-Al oligocations produced the corresponding cross-linked fluorhectorites, which showed markedly higher basal spacings (18.2–20.0 Å for air-dried samples), surface areas (~300–380 m2/g), and thermal stability, as compared with those of the cross-linked hectorites. The cross-linking agent applied in the synthesis of the hydroxy-Al hectorite and fluorhectorite products consisted of a solution of hydroxy-Al oligomers aged for periods of 7 to 27 days. A constant ratio of 2.0 mmole Al/g of smectite was used in all preparations. The high basal spacings and porosity of the newly synthesized products are consistent with a structure similar to that previously proposed for cross-linked hydroxy-Al montmorillonite.

The specific surface area, S, of a clay is commonly measured by the adsorption of ethylene glycol monoethyl ether (EGME); however, this method can be tedious and time consuming, especially if the clay is saturated with a monovalent, highly hydrated cation. An alternative method for measuring S was developed involving infrared internal reflectance spectroscopy. This method is based on the discovery that the ratio of R1, the reflectance of a clay-HOD mixture at the frequency of O-D stretching, to R2, the reflectance of the mixture at the frequency of H-O-D bending, is linearly related to S. The correlation coefficient between R1/R2 and S, as measured by the adsorption of EGME, was 0.995. Consequently, a calibration curve of R1/R2 versus S was constructed, and the measured values of R1/R2 for any clay-HOD mixture were referred to it for the determination of S. Results were obtained in triplicate in about an hour; hence, this method of determining S is more rapid and convenient than that involving the adsorption of EGME. Moreover, it applies to clays in a natural condition, i.e., swollen in water.

The modification of the external surface area and the two types of microporosity of palygorskite (structural and interfiber porosity) were examined as a function of the temperature of a vacuum thermal treatment to 500°C. The methods used included: controlled-transformation-rate thermal analysis, N2 and Ar low-temperature adsorption microcalorimetry, conventional and continuous gas-adsorption volumetry (for N2 and Ar) at 77 K and CO2 at 273 and 293 K, water vapor adsorption gravimetry, and immersion microcalorimetry in water. At temperatures < 100°C only 18% of the structural microporosity was available to N2, 13% to Ar, and 100% to CO2 at 273 K. In both experiments the channels filled at very low relative pressures. At temperatures between 70° and 130°C the structure folded, and the mineral transformed to anhydrous palygorskite, which showed no structural microporosity. The interfiber microporosity was found to be independent of the temperature treatment, and the external surface area decreased slightly from 65 to 54 m2/g. The water adsorption isotherms showed that the folding of the structure was reversible up to final outgassing temperatures >225°C.

This paper compares the texture of palygorskite after acid leaching with that of the product after extraction silica is removed. These effects were evaluated on the basis of nitrogen adsorption-desorption and mercury penetration porosimetry. Acid leaching at reflux temperature with 2 N HCl resulted in an increase in surface area from 138 to 399 m2/g, due to a partial (~50%) dissolution of the octahedral sheet and the creation of microporosity. This microporosity disappeared if the silica generated by the leaching was removed. The surface area also decreased from 399 to 214 m2/g, and the pore volume decreased from 0.538 to 0.507 cm3/g. The microporosity must therefore have been due to texture development in the generated silica.

Smectites exchanged to various degrees with mono- or biprotonated 1,4-diazobicyclo(2,2,2)-octane (Dabco) have a porous structure in which the organic molecule acts as a “pillar.” Less Dabco2+ than Dabco1+ was necessary both to initiate and to complete expansion, whereas for both Dabco1+ and Dabco2+ the threshold for expansion increased with the charge density of the clay. Interstratification of 9.7-Å and 14.5-Å (Dabco1+) or 14.1-Å (Dabco2+) layers was observed before full expansion occurred.

Nitrogen sorption isotherms on partially exchanged Dabco1+- and Dabco2+-clays are of the BET II and Langmuir type respectively, whereas n-butane adsorbed according to BET type II for both cationic forms. The specific surface area was governed by the number of Dabcoz+ pillars, irrespective of the inorganic cation, and increased with Dabcoz+ content even beyond the composition where full expansion was reached and notwithstanding the increasing number of silicate layers in the c direction of the crystal units. This relationship is explained by an enhanced random interleaving of clay platelets in the stacking units containing Dabcoz+.

The catalytic activity of sepiolite from Amboseli, Tanzania, for the dehydration and dehydrogenation of ethanol at 150°–300°C has been studied using a flow reactor. Both reactions occur, but the catalyst activity decreases with use. The products include water, carbon dioxide, ethene, ethanal (acetaldehyde), diethyl ether, but-1,3-diene, but-2-enal (crotonaldehyde), and an unidentified aromatic compound. The proportions change with temperature, the dehydrogenation reaction being favored at the higher temperatures. The BET surface areas of the sepiolite are 316 m2/g (nitrogen adsorption at — 197°C) and 212 m2/g (ethanol vapor adsorption at 25°C, assuming a molecular cross-sectional area of 24.6 Å2), indicating a possible greater penetration of pores and channels by nitrogen compared with ethanol vapor under these conditions. The pore-size distribution reveals that approximately 55% of the surface area measured by nitrogen adsorption is contributed by micropores.

The nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces.

Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.

Nineteen drill core samples of lower Dogger opalinum shale from wells drilled in connection with a tunnel project near Brugg, northern Switzerland, were investigated. The shale is a well known swelling rock that has caused problems in underground construction work. Swelling pressures determined under constant volume conditions to obtain maximum values were 0.7 to 2.2 N/mm2. The samples contained 37–59% clay-size material and about 35% quartz, 7–18% carbonate minerals, and about 5% feldspar, pyrite, and organic matter. In addition to kaolinite, illite, and chlorite, the clay-size fraction also contained mixed-layer illite/smectite with about 30% swelling layers. The specific surface area of the clay fraction was 135 m2/g. The specific surface charge of the clay (6.7 × 104 esu/cm2), the ion concentration in the pore fluid of the specimen after the swelling test (10−2 mmole/cm3), the valence of the ions in the double layer of the clay particles (+1), and the half distance between the clay plates in the specimen (8–15 Å) allowed the calculation of the swelling pressure for each sample according to the Gouy double layer theory.

The mean value of the calculated swelling pressures was found to be of the same order of magnitude as the measured values, indicating that the technique can be used where cylindrical or rectangular specimens are not available for direct measurement.

Modifications of the external surface area and the two types of microporosity of sepiolite (structural microporosity and inter-fiber porosity) were examined as a function of the temperature of a vacuum thermal treatment to 500°C. The methods used included: reciprocal thermal analysis, N2 and Ar low-temperature adsorption microcalorimetry, gas adsorption volumetry (for N2, Ar, and Kr at 77 K and CO2 at 273 and 293 K), water-vapor adsorption gravimetry, and immersion microcalorimetry into liquid water at 303 K. If the sample was not heated >100°C, only 20% of the structural microporosity was available to N2, whereas 52% was available to CO2 at 293 K. In both experiments, the channels filled at very low relative pressures. At >350°C, the structure transformed to anhydrous sepiolite, which showed no structural microporosity. The inter-fiber microporosity decreased from 0.031 to 0.025 cm3g (as seen with N2), and the external specific surface area decreased from 120 to 48 m2/g. The water adsorption isotherms showed a lower and lower affinity of the external surface of fibers for water as the temperature of thermal treatment increased. The thickness of the bound water on the external surface was estimated to be ≤ 3.5 monolayers, i.e., less than 10 Å.

The size distribution of unit particles of two New Zealand allophanes (An and Rh), in dilute (0.8% w/v) aqueous suspensions, has been determined by small-angle neutron scattering (SANS). In addition, the specific surface area of the samples was measured by ethylene glycol retention, and their morphology examined by high-resolution transmission electron microscopy (HRTEM). The SANS data indicate that although both allophanes are somewhat polydisperse, the average diameter of their unit particles is significantly different, being 56 and 43 Å for allophane-An and allophane-Rh, respectively. Consistent with this observation, the specific surface area of allophane-Rh (897 mVg) is appreciably greater than that of allophane-An (638 m2/g). Under the electron microscope, both samples appear as aggregates of hollow spherules but HRTEM did not clearly distinguish between the two allophanes in that the largest population of spherules had diameters near 50 Å. Because of the assumptions and uncertainties involved in the SANS and surface area measurements, the data must be discussed in terms of their respective ratios. On this basis, the spherule diameter ratio is of the same order of magnitude as the inverse ratio of specific surface area. The latter value is also in reasonably good agreement with the corresponding ratios of phosphate adsorption capacity and BET nitrogen areas, derived from earlier studies.

X-ray diffraction patterns of oriented films of montmorillonite containing enantiomeric tris(2,2′-bipyridyl) ruthenium(II) chloride (Ru(bpy)22+) show a peak corresponding to basal spacings of approximately 27 Å. This peak is absent from the X-ray patterns of montmorillonite films containing racemic cations. A basal spacing of 27 Å is consistent with the adsorption of 2 layers of the enantiomeric cations in each interlayer space. Under the same condition only one layer of the racemic cation was intercalated (basal spacings of 17.9 Å). These results are in accord with previous reports that montmorillonite can adsorb more of the optical isomers than of the racemic mixture of Ru(bpy)32+. Addition of NaCl to the mixtures resulted in an increase in the level of adsorption of the racemic cations and in the appearance of a peak at 27 Å in the X-ray pattern.

Adsorption calorimetry was used to develop a method for determining the surface area of low-surface-area materials (<1 m2/g), which required no pretreatment of the surface, such as outgassing at elevated temperatures. The method involved flowing heptane through a small amount of sample (0.15 to 1.0 g) in the flow cell of a commercial microcalorimeter. When thermal equilibrium was reached at the powder-heptane interface, pure heptane was replaced with a heptane carrier-solution containing 0.6 volume % n-butanol (n-BuOH) as the preferential adsorbate. The integral enthalpy of preferential saturation adsorption, ΔHsat, of n-BuOH on the surface was found to be a function of the BET surface area of the sample. An empirical relationship between ΔHsat and BET surface area was determined over a surface area range of about three orders of magnitude (0.095 to 81 m2/g) by performing adsorption experiments on five α-alumina standard reference powders. The technique was applied to the determination of surface areas of untreated rock and mineral powders.

To determine the parameters that control the attack of Mn minerals by acid ammonium oxalate in darkness (AAOD), rhodochrosite, pyrolusite, manganosite, hausmannite, and bixbyite were shaken with AAOD for 2 hr. These treatments were followed systematically by X-ray powder diffraction (XRD) and AAOD-extractable Mn analyses. About 5% of original hausmannite (surface area = 6 m2/g) remained in the solid residue of the AAOD treatment; however, if the hausmannite surface area was increased to 8 m2/g, by grinding, it completely dissolved in oxalate. Synthetic hausmannite of high surface area (37 m2/g) and rhodochrosite were completely dissolved by oxalate. Manganosite (1.5 m2/g) and especially pyrolusite (~ 1 m2/g) were more resistant to AAOD attack. Ground manganosite (4.2 m2/g) dissolved completely, but ground pyrolusite (7.2 m2/g) was only partially attacked by AAOD, inasmuch as about 25% of pyrolusite was found in the residue. An increase of the extraction time to 4 hr did not completely dissolve the ground pyrolusite.

As a result of the AAOD treatment, MnC2O4 · 3H2O and MnC2O4 · 2H2O precipitated from the oxalate solutions with all starting minerals, except pyrolusite (~ 1 m2/g), which only slightly dissolved. The seldom reported MnC2O4 · 3H2O phase was identified in residues of freshly extracted samples by its strong characteristic peak at 6.5.-6.6 Å, the intensity of which gradually decreased and disappeared over several days when the sample was exposed to ambient conditions (22°C and 70% relative humidity). The trihydrate phase also collapsed after heating AAOD-treated rhodochrosite at 50°C; α-MnC2O4 · 2H2O was identified as the main crystalline product. Heating the α-MnC2O4 · 2H2O product at 115°C overnight transformed most of it to MnC2O4. The color of the oxalate-treated samples ranged from pinkish-gray to black (7.5 YR); their surface area ranged from about 20 to 30 m2/g. The degree of transformation of Mn minerals by oxalate depended on the surface area and structural characteristics of the starting materials.

Synthetic 2-line and 6-line ferrihydrite samples prepared from ferric nitrate solutions have the bulk compositions Fe4(O,OH,H2O)12 and Fe4,6(O,OH,H2O)12, respectively. The composition depends on crystal size, which averages 20 Å for 2-line and 35 Å for 6-line ferrihydrite. X-ray absorption edge spectra indicate the presence of tetrahedral Fe3+, a conclusion supported by heating experiments which show the development of maghemite after heating to 300°C in the presence of N2, followed by the formation of hematite at higher temperatures. These two reactions are recorded on differential thermal analysis traces by exotherms at 350° and 450°C. Transmission electron microscopy shows that 2-line ferrihydrite has no Z-axis regularity but does show hexagonal 2.54-Å lattice fringes. Six-line ferrihydrite forms faceted crystals having 9.4-Å c-parameter only detectable in dark field. In bright field, 2.54-Å lattice fringes indicate greater atomic regularity than in 2-line ferrihydrite. Analysis of the X-ray powder diffraction pattern of 6-line ferrihydrite suggests a structure based on double-hexagonal close-packed oxygens, containing 36% Fe in tetrahedral sites. Selective chemical dissolution, surface area measurements, and magnetic susceptibility are consistent with the recorded properties of ferrihydrite.

The effect of Fe oxidation state on the surface charge (CEC) and solubility of smectites were studied using the <2-μm, Na+-saturated fraction of an Upton, Wyoming; a Czechoslovakian; and a New Zealand montmorillonite; and a Garfield, Washington, nontronite. The reduction of structural Fe3+ in the octahedral sheet of each clay produced a net increase in the negative surface charge of the clay. The observed cation-exchange capacities deviated from the linear relationship predicted by charge-deficit calculations, assuming changes only in the Fe2+/Fe3+ ratio, and reversibly followed Fe reduction according to a 2nd-degree polynomial function. The deviations suggest reversible changes in mineral structure and composition during Fe reduction.

These clays were susceptible to partial dissolution in citrate bicarbonate (CB) and citrate-bicarbonate-dithionite (CBD) solutions. Small amounts of Fe and Si dissolved as a result of Fe reduction in CBD, but affected <1% of the total clay mass except for the Czechoslovakian clay in which 2% of the clay dissolved. Although slightly more Fe dissolved than Si, no change in surface charge was noted. Almost no dissolution of these elements was detected in CB solution. In contrast, significant Al was detected in the CB solution, suggesting a heterogeneous dissolution mechanism. The CEC, however, was unchanged by the CB treatment. These results may be explained by the adsorption of hydrogen ions into the vacated Al3+ sites in the mineral structure. Dissolution seems to have been independent of the effects of Fe oxidation state on surface charge.