Polynuclear hydroxy-Al cations were prepared by partially neutralizing dilute solutions of aluminum chloride. These cations were introduced in the interlayer space of montmorillonite by cation exchange, which formed heat-stable pillars between the silicate layers. Polynuclear hydroxy-Al was preferentially adsorbed on montmorillonite compared with monomer-Al; the maximum amount adsorbed was ∼400 meq/100 g of montmorillonite. Of this amount 320 meq was non-exchangeable. The 001 X-ray powder diffraction reflection of the polynuclear hydroxy-Al-montmorillonite complex was at 27 Å, with four additional higher-order basal reflections, giving an average d(001) value of 28.4 Å. This complex was thermally stable to 700°C. An analysis of the basal reflections by the Fourier transform method indicated that the 28-Å complex had a relatively regular interstratified structure of 9.6- and 18.9-Å component layers with a mixing ratio of 0.46:0.54. This ratio implies that the hydroxy-Al pillars occupied every second layer. Considering the relatively small amount of Al adsorbed and the thermally stable nature of the structure, the hydroxy-Al pillars must have been sparsely but homogeneously distributed in the interlayer space.

Reactions between hydroxy-Al ions and orthosilicic acid as influenced by citric acid were studied at an initial Si concentration of 1.6 × 10−3 M, Si/Al molar ratios of 0.5 and 1.0, OH/Al molar ratios of 1.0-3.0, and citric acid/Al molar ratios of 0-0.3. In the absence of citric acid and at OH/A1 ratios of 1.0-2.8, imogolite (>0.01 μm) was dominant in the precipitates. At citric acid/Al ratios of 0.01-0.1, imogolite and/or pseudoboehmite were dominant in the precipitates at OH/Al ratios of 1.0 and 2.0, and imogolite and/or ill-defined aluminosilicate complexes at OH/Al ratio of 2.8. Instead of allophane or “proto-imogolite” allophane being the predominant species in the precipitates, the formation of ill-defined aluminosilicate complexes at OH/Al ratio of 3.0 was steadily promoted by increasing the solution citric acid/Al ratios from 0 to 0.3. The freeze-dried soluble products (<0.01 μ) ranged from silica gel to “proto-imogolite,” depending upon the basicity of Al and the level of citric acid of the parent solution. The amount of “proto-imogolite” increased with increasing citric acid/Al ratios from 0 to 0.1 in solution. Complexing low molecular weight organic acids, such as citric acid, impeded the formation of the short-range ordered aluminosilicates, allophanes and imogolite.

Reaction of hydroxy-Al oligocations with Ce3+- and La3+-exchanged montmorillonites, using 1.25, 1.60, or 2.0 mmole Al/g smectite, yielded partially pillared hydroxy-Al montmorillonite products containing a significant concentration of residual Ce3+ or La3+. After heat treatment at 250°C these products showed high surface areas (∼340–500 m2/g) and high basal X-ray powder diffraction spacings (18.0–18.6 Å). Calcination at 400°–700°C resulted in lower surface areas of ∼200–450 m2/g and basal spacings of 16.3–18.3 Å, the values showing a gradual decrease with a decrease in the Al/smectite weight ratio and/or increase in the heat-treatment temperature. A major modification and improvement in the cross-linking procedure was achieved by fast aging (6–48 hr) of the hydroxy-Al oligomeric solution at 95°–100°C, instead of conventional aging for 2–3 weeks at 25°C.

Fluorinated NH4+-montmorillonites, containing 0.4 to 2.1 wt. % F, were prepared by reaction of NH4+-montmorillonite at 60°C with 1.0 to 3.0 N aqueous solutions of NH4F. Interaction of the fluorinated montmorillonites with hydroxy-Al oligocations, using a ratio of 2.0 mmole Al/g smectite, yielded a series of cross-linked fluorinated montmorillonites with basal spacings of 17.9–18.0 Å and surface areas of 180–325 m2/g after heat treatment at 250°C. Calcination at 400°–500°C resulted in lower d(001) (16.6–17.7 Å) and surface-area values (140–300 m2/g). Increase in the fluorine content caused gradual decrease in both values. Transmission electron microscopy of pillared Ce-montmorillonite showed a highly oriented network of well-separated, parallel unit layers with an interlayer distance, Δd(001), of 9–10 Å. Calculated lateral (interpillar) distances were in good agreement with the pore-size distributions determined in independent adsorption studies.

Chloritic veins in serpentinite and their weathering products were analyzed by X-ray powder diffraction (XRD) and X-ray fluorescence spectrometry (XRF). Chlorite formed during the Hercynian-age orogenesis had apparently been partly transformed to high-charge vermiculite during subsequent metamorphism of the rocks. The idealized structural formulae for these minerals are (Al1.9Fe3+0.2Fe2+0.4Mg9.2Cr0.2)(Si5.8Al2.2)O20(OH)16 and X1.3(Fe3+0.7Fe2+0.1Mg5.2Ni0.1)(Si5.8Al2.2)O20(OH)4, respectively. This transformation appears to have taken place by the removal of the hydroxy-interlayer from the chlorite without major effect on the rest of the structure. It is not clear whether other hydroxy-interlayered vermiculites containing less tetrahedral aluminum were intermediate weathering products or inherited minerals. The ultimate weathering product of chlorite and vermiculites was a Fe3+-rich smectite, which probably formed by precipitation from solution.

Three montmorillonite samples, from Wyoming (particle size <0.2 µm, 4.6 wt. % Fe2O3), Greece (<14 µm, 6.5 wt. % Fe2O3), and Poland (0.5 wt. % Fe2O3, two fractions <2 µm and 2–10 µm) were intercalated with hydroxy-Al species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 wt. % Al2O3 for 0.2 µm in size to 22.6 wt. % for >2 µm. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80°C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 Å. The diffusion of the Al cations therefore limited the cation-exchange process. The addition of NH4+ to the pillaring solution decreased the amount of Al fixed by the clay from 31 (no NH4+ to 26 wt. % (NH4+/Al = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4+ and Al-hydroxy cations for ion-exchange sites forced the Al species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Al exchanged was then reduced. After calcination in air at 700°C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4+ was added, compared with 0.11 ml/g for a NH4+/Al ratio of 10. The Fe content of the clay affected the thermal stability of pillared clays at 800°C: for two samples prepared by competitive ion exchange (NH4+/Al = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe2O3 to 0.08 ml/g for 0.5 wt. % Fe2O3. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150°C, on samples calcined at 500°C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.

The treatment of smectites with a hydroxy-Al polymer produced chemically modified clays that had much greater affinities for chlorinated dioxins and biphenyls than untreated clays. For hydroxy-Al-treated kaolinite, the high affinity for chlorinated dioxins is thought to have arisen from an interaction between the hydroxy-Al polymer bound to the clay and the chlorinated dioxin in solution. Thus, the adsorption of dioxins from aqueous solution by hydroxy-Al-treated clays is similar to the adsorption of reactants from the gas phase by metals supported on mineral oxides during catalysis. In both systems, the essentially inert mineral oxide support effectively disperses the active adsorptive agent. At the concentrations of octachlorodioxin used in this study (≤5 ppb), hydroxy-Al-montmorillonite had a distribution coefficient of 90,000 (ml/g), corresponding to about 95% removal efficiency of the dioxin from solution per batch. For hexachlorohiphenyl, the distribution coefficient was 30,000 (ml/g), and the removal efficiency was 85%.

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.

Beidellite was synthesized hydrothermally from a noncrystalline gel at 320°C and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4+-exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/Al molar ratios. The solutions were investigated by several methods, including 27Al nuclear magnetic resonance. Essentially, two Al species were detected: monomelic Al and a polymerized form containing Al in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 Å at 110°C and 16.2 Å at 700°C. The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Brönsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.

Due to their unique polarity, pore-size distribution, and high surface areas, pillared and delaminated clays are potentially useful materials for the adsorption of environmental toxicants. To determine their properties for adsorption of chlorinated phenols, alumina-pillared montmorillonite (APM), chromia-pillared montmorillonite (CPM), and alumina-delaminated Laponite (ADL) were reacted with aqueous pentachlorophenol (PCP) solutions in batch equilibrium experiments. An hydroxy-Al Laponite (HAL) in which the Na+ exchange ions were replaced by ions of the type Al13O4(OH)(24+x)(H2O)(12-x)(7-x)+ was included in the study. With ADL as the adsorbent, the extent of PCP adsorption increased with decreasing pH, and then became constant at pH ≤ pKa. Thus, the neutral phenol was preferred over the phenolate form. Binding of neutral PCP at pH 4.7 to all adsorbents never reached saturation values, and the loadings achieved were limited by the water solubility of the adsorbate. Among the pillared and delaminated clays investigated, ADL exhibited the largest capacity for physical adsorption of PCP at pH 4.7. Differences in the PCP binding capacities for APM, CPM, and ADL suggested that adsorption was dependent on the pore structure and surface composition of the modified clay adsorbent, not on surface area alone. HAL exhibited quantitative uptake of PCP at the 8 µmole/g level, indicating that a chemi-sorption mechanism may operate for PCP binding to this adsorbent. Adsorption of 3-chlorophenol, 3,5-dichlorophenol, and 3,4,5-trichlorophenol by ADL at pH 7.4 increased as the degree of hydrophobicity and chlorination of the phenol increased; hence, the binding capacity was not limited by the molecular size of the adsorbate. In contrast to the adsorption properties observed for pillared, delaminated, and hydroxy-interlayered clays, Na+-montmorillonite and Na+-Laponite did not adsorb PCP from aqueous solution.

Hydroxy-Al-montmorillonite was prepared by mixing Na-Wyoming montmorillonite with Al(OH)2.5 polycations and aging the mixture for 10 days. The reactions of this complex with citric acid at millimolar concentrations were investigated at different pHs for a 4-hr reaction time. The citrate sorption data, X-ray powder diffraction patterns of the montmorillonite adsorbent, and solubility products for Al(OH)3, estimated after computer speciation of the aqueous solution phase, suggested two reaction mechanisms, depending on pH. At 4 < pH < 5.5, the complex was stable, and only external hydroxy-Al polycations could react with citrate, yielding a sorption envelope characteristic of an acid having a low pKa. At higher pH, and particularly at pH > 7, the interlayer Al-polymers became accessible to the ligand and desorbed quickly from the montmorillonite basal planes to form a new, external, X-ray-amorphous solid phase with citrate. This reaction produced a large second peak in the sorption envelopes near pH 8, which was controlled by the increasingly negative surface charge at high pH and by the initial concentration of citric acid. This ligand accelerated, i.e., favored kinetically, the dissociation of adsorbed hydroxy-Al polymers from montmorillonite at pH > 7.

The sintering of montmorillonites pillared by hydroxy-Al species was investigated by several techniques. The change of the microporosity of the pillared interlayer clay with temperature shows that sintering was mainly due to the loss of microporosity. On calcination of the parent clay at 760°C, the X-ray powder diffraction pattern did not change; the 060 line shifted only slightly from 8.988 to 9.017 Å. The infrared (IR) spectrum suggested some dehydroxylation, but the structure appears to have been preserved. On calcination of the pillared clay at >700°C, the intensity of the 001 line decreased steadily, the 060 line broadened, and the b parameter decreased slightly from 8.988 to 8.928 Å. Fe3+ ions apparently occupied only one site after calcination at 300°C and two sites after calcination at 700°C. Smaller isomer shifts and higher quadrupole splittings in the Mössbauer spectra suggest that calcination produced more covalent bonding of Fe3+ and a highly distorted structure. The IR spectrum was significantly modified by calcination of the sample, and the 935- and 1125-cm−1 bands disappeared and the 1035-cm−1 band broadened. These results suggest that at <700°C the pillars sintered and that the clay progressively decomposed at >750°C. The pillaring-induced decrease of thermal stability of the clay was likely due to the introduction of protons during the first step of the preparation. The thermal stability of these Al-pillared interlayer complexes is comparable to that reported for hydroxy-silicoaluminum montmorillonites and fluorhectorites.

Weathering has etched and deeply-denticulated the constituent orthopyroxenes, and chlorite has been transformed to vermiculite in the upper 3 m of an aeolian, periglacial sand dune formed in northeastern Indiana about 13,000 b.p. Pyroxene weathering begins with the development of cleavage-parallel etch pits on {010} and {100} surfaces. These pits coalesce and eventually crop out on basal surfaces as denticulations. The mean denticulation size increases logarithmically toward the surface, and the denticulation size of the orthopyroxenes is a quantifiable feature of the weathering process. Ferruginous pendants, microboxworks of iron oxides, and other indications of iron redeposition within the ortho-pyroxene microenvironments were not observed.

Chlorite in the dune has been weathered to vermiculite. The parent chlorite is a high-Fe variety, and the transformation to vermiculate does not involve the development of a chlorite/vermiculite intermediary phase. Fe2+ is oxidized as part of the transformation process and this iron is retained in the sediment as discrete goethite and as crystalline and noncrystalline coatings on the dune grains. The vermiculite from depths shallower than 64 cm is only partly expandable and is completely collapsed by K-saturation or heat treatment. This is a hydroxy-Al vermiculite and its formation is typical of intense weathering under the acid conditions prevalent at the dune surface.

A study was carried out on the influence of the sequence of addition of montmorillonite, hydroxy-Al ions, and tannic acid ([Al] = 0.015 M; 6 mmole Al/g of clay; tannic acid/Al molar ratio = 0.1) on the nature of organo-clay complexes formed at pH 4.5. A negligible amount of tannate was held on the clay surfaces in the absence of Al, whereas in the presence of Al, hydroxy-Al-tannate species were easily adsorbed on clay surfaces. Their distribution on the external surface and in the interlayer space of montmorillonite, however, was a consequence of how the components reacted with each other. The complexes showed broad X-ray powder diffraction peaks at 15.6 to 19.2 Å at room temperature. They also showed different behavior to preheating, ethylene glycol solvation, and chemical treatments. Whereas tannic acid showed two prominent exothermic peaks at 390° and 510°C, all hydroxy-Al-tannate-mont-morillonite complexes showed a broad exotherm at about 400°–450°C. Some complexes showed, in addition, a small inflection between 350° and 420°C. The complexes also showed distinct differences in cation-exchange capacity, carbon content, extractable Al, titratable acidity, and mode of aggregation after drying.

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

Quasi-spherical particles (7-µm mean diameter) were prepared from cross-linked hydroxy-Al-montmorillonite (basal spacing =15.3 and 18.6 Å) by spray-drying. These particles (SP-CLM) were used as a packing material for columns in high-pressure liquid chromatography (HPLC). Aromatic phosphate esters, chlorosubstituted phenyl-ureas, monosubstituted benzenes, and the o-, m-, and p-isomers of disubstituted benzenes were separated on the columns, using isopropanol and hexane. Alkyl and alkoxy groups in the solute molecules sterically hindered the interaction of these molecules with the solid phase. The retention of the isomers of disubstituted benzenes that possess one electronegative (or dipolar) and one nonpolar substituent increased in the order: o- < m- < p-. In contrast, for all investigated disubstituted benzenes containing two electronegative (or dipolar) substituents, the o-isomer was retained on the 18.6-Å SP-CLM more strongly than the m- and p-isomers. The chromatographic data suggest that the strength of the interaction of phenolic groups with the solid phase increased with the acidity of these groups. The o-isomers of phenols that contained an additional electronegative (or dipolar) substituent displayed an exceptionally strong adsorption. The capacity of the o-isomers of disubstituted benzenes containing two electronegative (or dipolar) substituents to form chelates with Al probably was responsible for the strong retention of such o-isomers compared with the retention of the corresponding m- and p-isomers.

Cross-linked hydroxy-Al-montmorillonite acted as a strong and selective adsorbent for many families of organic compounds. It was used successfully as the solid phase in HPLC separations with eluents ranging from nonpolar (e.g., hexane) to highly polar (e.g., water).

The clay and bulk mineralogy of soil and till from 26 Adirondack watersheds was studied. The materials consist typically of quartz, K-feldspar, plagioclase, mica, vermiculite, and kaolinite. Talc, smectite, halloysite, and hornblende are present in some samples. The clay fraction of the soils is composed predominantly of vermiculite, likely derived from the transformation of a mica precursor, and kaolinite. The soil vermiculite commonly contains hydroxy-Al interlayers which are especially prevalent in the B-horizon samples. Despite significant variation in the type of bedrock and the composition of heavy mineral assemblages in these watersheds, the clay mineralogy is remarkably uniform. This finding supports earlier suggestions that the occurrence of vermiculite in soils is more dependent on climate than on the nature of the parent material.

Water-infiltration characteristics of soil can be improved by preventing clay dispersion. The present study determined the adsorption properties of hydroxy-Al polycations (Al-p) and their relation to the destabilization of clay suspensions. Al-p was synthesized and fractionated into nominal molecular weights between 104 and 5 × 104. The reactions of Al-p with Na-illite and Na-montmorillonite indicated a very strong affinity of Al-p to the clay surfaces. The maximum adsorptions of Al-p by Na-illite and Na-montmorillonite were found to be 0.37 and 1.7 mmole Al/g, and very close to the cation-exchange capacity of the two clays, suggesting that the adsorption was chiefly controlled by the mechanism of charge screening. Adsorption of Al-p increased the points of zero charge (PZCs) and the apparent points of zero salt effect (PZSEs) of illite and montmorillonite. PZSEs for both clays were 4.7 at their maximum Al-p adsorption, and PZCs ranged from 5.3 to 6.4, depending on solution ionic strength and the individual clay minerals. The differences in PZCs were probably due to outer-sphere complex formation between Al-p-treated illite and montmorillonite and the swamping electrolyte. Critical flocculation concentrations (CFCs) of Al-p for Na-illite and Na-montmorillonite were at 0.28 and 1.0 mmole Al/g, whereas zero electrophoretic mobilities were at about 0.36 and 1.67 mmole Al/g Al-p additions. Excessive addition of Al-p reversed this surface charge of clay colloids and restabilized the illite but not montmorillonite suspensions. This difference was probably due to the stronger and more extensive interparticle bridging of montmorillonite particles by Al-p than those of illite. The CFCs for the two clays were also found to be dependent on sodium adsorption ratio (SAR), pH, and ionic strength. Increases in SAR and pH significantly increased the CFC, whereas an increase in ionic strength decreased the CFC.

Hydroxyaluminosilicate (HAS) ions prepared from hydroxy-Al (HyA) ions and orthosilicic acid at different NaOH/Al molar and Si/Al atomic ratios were fixed in the interlayer spaces of vermiculite (Vt). The electric charge and surface characteristics of HAS-Vt and HyA-Vt complexes formed were investigated in the pH range of 4 to 8. At pH 4 to 6, the magnitude of negative charge (CEC) of HAS-Vt and HyA-Vt complexes was drastically reduced by a HAS- or HyA-interlayer formation of Vt. At pH 7 to 8, especially in NaOH/Al molar ratio of 2.5, the magnitude of negative charge was from 62 to 89% of CEC in untreated Vt, suggesting that part of HAS or HyA ions fixed on Vt was excluded from its interlayer spaces. The positive charge did not develop on HAS-Vt and HyA-Vt complexes at pH between 4 and 8. The fixation of HAS or HyA ions on Vt caused the significant reduction of its total and internal surface areas as well as the slight increase of its external surface area. The HAS- or HyA-fixation in the interlayer spaces of Vt was confirmed by X-ray diffraction analysis. Our results provided evidence of a possibility that Vt could fix HAS ions in the same way as HyA ions, transforming to chloritized-Vt. These interlayer materials could play a significant role in modifying the surface and mineralogical properties and cation exchange capacity of clays and soils.