Showing papers in "Clays and Clay Minerals in 1985"

Properties of Goethites of Varying Crystallinity

Abstract: Goethites were synthesized from ferrihydrite in 0.7 M KOH between 4° and 90°C. As temperatures increased, the goethite crystals became larger and of less domainic character, and surface areas decreased from 153 to 9 m2/g. Surface area, oxalate-soluble Fe to total Fe ratios, chemisorbed water, Mossbauer parameters, and dissolution rate in 6 M HCl at 25°C are particle-size controlled, whereas mean crystallite dimensions, a-dimension of the unit cell, differences between the two OH-bending modes, and dehydroxylation temperatures suggest the existence of a low-temperature (high-a-dimension) and a high-temperature (low-a-dimension) goethite, with a narrow transition range at a synthesis temperature of 40°–50°C. Hydrothermal treatment at 125°–180°C of a low-temperature goethite led to a healing of the multidomainic, microporous high-a-dimension goethite into a monodomainic low-a-dimension goethite of similar overall crystal size with the properties of a low-a-dimension goethite.

Crystal Structure of Kaolinite: Dimethylsulfoxide Intercalate

Abstract: The crystal structure of the kaolinite : dimethylsulfoxide (DMSO) intercalate (P 1, a = 5.187(2), b = 8.964(3), c = 11.838(4) A, a = 91.53(1) ~ = 108.59(2) ~ T = 89.92(1)*) has been determined using spectroscopic and X-ray and neutron powder diffraction data. Both the X-ray and neutron powder diffraction patterns were refined. Solid-state ~3C, 298i, and 27A1 nuclear magnetic resonance data and previously collected infrared spectroscopic data provided a useful starting model for structural refinement. Due to the extreme overlap of reflections of this low-symmetry unit cell, the Rietveld method proved inadequate, and quasi-single crystal methods were employed. Each DMSO molecule was found to be triply hydrogen bonded above the octahedral vacancy in the glbbsitic sheet of the kaolinite layer. One methyl group is keyed into the ditrigonal hole in the tetrahedral sheet with the other S--C bond parallel to the sheet. The DMSO molecules are accommodated by significant horizontal displacement of individual kaolinite layers to achieve almost perfect overlap of the octahedral vacancy by the adjacent ditrigonal hole.

Transmission electron microscopic study of diagenetic chlorite in Gulf Coast argillaceous sediments

Abstract: Transmission and analytical electron microscopy have been used to study the diagenesis of the trioctahedral component of phyllosilicates (principally chlorite) in argillaceous core samples (depths of 1750, 2450, and 5500 m) from the Gulf Coast. Chlorite was observed as 100-150-A thick packets intergrown within mixed-layer illite/smectite in the 2450-m sample and was more abundant and larger in packet thickness in the 5500-m sample. The chlorite is disordered in stacking sequence as characterized by diffuseness of reflections with k ≠ 3n in electron diffraction patterns. Berthierine (7-A) was locally found to be intercalated within chlorite layers. Chlorite from the 5500-m sample is iron-rich and has an average chemical formula of Fe3.1Mg1.1Al2.7Si2.8O10(OH)8. This chemical composition and textural relations suggest that the chlorite formed within mixed-layer illite/smectite utilizing Fe and Mg released from the smectite during its conversion to illite. The berthierine is nearly identical in chemical composition with the coexisting chlorite although it may have a slightly higher Fe content. The 7-A berthierine is probably a metastable precursor of the chlorite and may be diagnostic of the diagenetic environment.

Mineralogical and Morphological Evidence for the Formation of Illite at the Expense of Illite/Smectite

Abstract: The conversion of smectite to illite by way of a mixed-layer illite/smectite (I/S) series was found to be the major depth-related reaction in clay-mineral assemblages from two cored sedimentary sequences in the Rocky Mountains. The I/S reaction occurred in both interbedded sandstone and shale of Upper Cretaceous and lower Tertiary age in the Green River basin, Wyoming, and in chalk and chalky shale of the Upper Cretaceous Niobrara Formation, Denver basin, Colorado. As the proportion of illite layers in I/S increased with depth in these rocks, the amount of I/S in the clay fraction decreased, and the amount of discrete illite increased. Scanning electron microscopy revealed that the morphologies of highly expansible, randomly interstratified I/S clay (samples from shallow cores) exhibited no distinctive intergrowth or overgrowth textures. In deeply buried rocks containing highly illitic, ordered I/S and abundant discrete illite, however, fibers or laths of illite were formed on earlier I/S substrates. Less commonly, I/S of low expandability shows morphological features of both smectite and illite whereby rigid laths of illite appear to have formed diagenetically from the wall surfaces of I/S honeycombs. This combined morphology suggests some dissolution and reprecipitation (or some reorganization) of materials from the I/S substrate as the substrate was transformed into a more illitic mixed-layer clay.

Development of layer charge and kinetics of experimental smectite alteration

Abstract: Sodium-saturated Wyoming bentonite was hydrothermally reacted at 150 ~ and 250~ for 30 to 180 days to determine smectite alteration rates that might be applied to nuclear-waste repository design. Na-Ca solutions deficient in K were used to determine the role of interlayer cations in the creation of high layer-charge in the smectites. The results provide insight into the mechanism and timing of various steps in the diagenetic alteration of smectite to illite. X-ray powder diffraction (XRD) analyses of the reacted clay showed little effect on the character of the 17-/~ reflection even after 180 days at 250~ Potassium saturation of these reacted clays and re-examination by XRD indicated collapse of some smectite layers, leaving at most only 60% expandable layers. The development of layer charge sufficient to cause collapse on saturation with a low hydration energy exchange-cation does not require K in the reacting fluid. Rate constants for the illitization reactions as determined by K-saturated collapse are between 1.0 x 10 -3 and 2.8 x 10-3/day with activation energies <3.5 kcal/mole. Ca in a Na-silicate- bicarbonate solution slightly reduced the illitizafion rate constants. These rate constants are higher than expected from extrapolation of studies of beidellite-composition glasses at higher temperatures, but lower than values obtained in studies of natural clays in artificial sea water. The release of Si, A1, and Mg in the 150~ experiments suggests congruent dissolution of the smectite. In contrast, at 250~ the release of A1 was not stoichiometric with Si; as little as one half of the relative available Si was released. Rather than different mechanisms for dissolution at the two temperatures, the conclusion is that noncrystalline Al-rich phases formed at greater rates at higher temperatures. The cation-exchange capacities for several of these reacted smectites were significantly less than expected, suggesting a clogging of interlayer sites, perhaps by Al-complexes.

Effect of solution conditions on the proportion and morphology of goethite formed from ferrihydrite

Abstract: In alkaline media and at 70°C dilute suspensions of ferrihydrite transformed to goethite between pH 112 and 14 and to a mixture of goethite and hematite above and below this pH range Increasing the temperature of the transformation or the concentration of the suspension reduced the pH range in which goethite alone formed The morphology of goethite was chiefly a function of the pH of the system Acicular crystals formed at all pHs and exclusively above pH 122 Epitaxial twinned crystals predominated at pHs below 11, and twins free from hematite formed at higher pHs Increasing the suspension concentration, ionic strength, or temperature extended the pH range over which twinned crystals formed Electron micrographs showed that twins formed mainly during the initial stage of the transformation, whereas acicular crystals formed over a longer period Thus, the twins appeared to nucleate in the ferrihydrite; nucleation of acicular particles took place in solution

Influence of Inorganic and Organic Ligands on the Formation of Aluminum Hydroxides and Oxyhydroxides

Abstract: Hydroxide and oxyhydroxide products of aluminum were formed at room temperature at an initial Al concentration of 2 × 10-3 M, pH 8.2, and at varying concentrations of organic and inorganic ligands commonly found in nature. The effectiveness of the ligands in promoting the formation of noncrystalline products over crystalline Al(OH)3 polymorphs was found to be in the following order: phthalate ≅ succinate < glutamate < aspartate < oxalate < silicate ≅ fluoride < phosphate < salicylate ≅ malate < tannate < citrate < tartrate. The lowest ligand/Al molar ratio at which the production of Al hydroxides or oxyhydroxides was inhibited ranged from 0.02 to 15. Above critical ligand/Al ratios, crystalline products were inhibited and ligands coprecipitated with noncrystalline products which remained unchanged for at least 5 months. Polydentate and large ligands generally were more inhibitive than those with fewer functional groups or of smaller size.

Raman spectroscopic study of kaolinite in aqueous suspension

Abstract: The vibrational modes of clay minerals in aqueous suspension are uniquely accessible to Raman spectroscopy, but this potentially powerful approach has not been applied heretofore to study clays in aqueous samples. In this paper, Raman spectra in the 100- to 4000-cm-~ region were obtained for kaolinite in aqueous suspension and in air-dry samples. Contact with water perturbed the low-wavenumber Raman spectrum (100 to 1000 cm -~) significantly with respect to relative band intensities and resulted in a pH dependence of the integrated intensity in the OH-stretching region. Comparison of the Raman and infrared OR) spectra of air-dry kaolinite samples confirmed five Raman-active OH-stretching modes at 3621, 3652, 3668, 3688, and 3696 cm -~, in contrast to four IR-active modes at 3621, 3652, 3668, and 3695 cm -t. The Raman spectra of two kaolinites of different origin showed differences in band positions and intensities. These results suggest that Raman spectroscopy may provide a useful method to study clay mineral-water interactions, colloidal behavior in clay suspensions, and variations in clay mineral structure.

Interaction of aliphatic amines with montmorillonite to enhance adsorption of organic pollutants

Abstract: X-ray powder diffraction studies were performed with propyl-, dodecyl-, and dodecyldiam- monium bentonites saturated with aqueous mixtures of eleven organic pollutants at concentrations of 0.01 to 100%. The alkylammonium salt treatment separated the montmorillonite unit layers, which increased the interlamellar volume and exposed the interlamellar surfaces for adsorption of the organic pollutants. Washing the salt-treated clays with distilled water removed excess, physically adsorbed al- kylammonium ions that could interfere with adsorption of the organic pollutants. Adsorption isotherms conducted at organic pollutant concentrations of 100 and I000 rag/liter indicated the three alkylam- monium montmorillonites, especially propylammonium montmorillonite, were effective adsorbents from aqueous solution, but to a lesser extent than adsorbents currently used in the water and wastewater fields.

Interlayer structures of the two-layer hydrates of Na- and Ca-vermiculites

Abstract: The three-dimensional order shown by the two-layer hydrates of Na- and Ca-vermiculite, prepared from Mg-vermiculite from Llano, Texas, has enabled clear, two-dimensional Fourier projections of their interlayer structures to be obtained. Structure factor calculations were made in space group C2 and with unit-cell dimensions of a = 5.358 A, b = 9.232 A, and s = 96.82°; for Na-vermiculite C = 14.96 A and for Ca-vermiculite c = 15.00 A. In Na-vermiculite the interlayer cations are octahedrally coordinated to water molecules with the sodium-water polyhedra only located between the triads of oxygen atoms forming bases to tetrahedra in adjacent silicate layers. In Ca-vermiculite the interlayer cations are in both octahedral and 8-fold (distorted cubic) coordination with water molecules. The octahedrally coordinated Ca ions are between the bases of tetrahedra in adjacent silicate layers, but the 8-fold coordinated Ca ions are between the ditrigonal cavities. In both Na- and Ca-vermiculite some water molecules are drawn from planar networks appreciably towards the ditrigonal cavities. The three-dimensional order observed for these vermiculites contrasts with the stacking disorder reported for Mg-vermiculite from Llano. The distinct crystallographic behavior of Na+, Ca2+, and Mg2+ in the hydration layers of Llano vermiculite probably depends on cation sizes and field strengths, together with the need to achieve local charge balance near the sites of tetrahedral Al-for-Si substitution.

Small-angle x-ray powder diffraction, morphology, and structure of allophane and imogolite

Abstract: Small-angle X-ray powder diffraction analyses and high-resolution electron microscopy of allophane samples (SiOJAlzO3 ratio, 1.12 to 1.68) showed that allophanes consist of nearly identical spherical particles with diameters of about 40 A and retain their characteristic "hollow" spherical mor- phology at different ambient moisture and even after dehydroxylation by heating at 500* to 6000C. Unheated allophane samples gave another X-ray powder diffraction band whose maximum position varied from 12.3 to 14.5 A depending on their SIO2/A1203 ratio. The appearance of this band may denote some long-range ordering in the structure of allophane. Unlike the spherical particles of allophane, the tube unit of imogolite collapsed on dehydroxylation. This observation suggests that imogolite and allo- phane are different in their framework structures and that a Si- or Si(A1)-tetrahedral sheet rather than an Al-octahedral sheet constitutes the framework structure ofallophane, irrespective of its SiO~/A12Oa ratio. 500 ~;WU 600~ ~,~/I~ OH /~G~'~X*o, ~�9 "~" ~r162 ~-~L~?Co }J~,DCg)o~o?~Y~" Y-~-2~d~O)~J

CROSS-LINKED SMECTITES. IV. PREPARATION AND PROPERTIES OF HYDROXYALUMINUM- PILLARED Ce- AND La-MONTMORILLONITES AND FLUORINATED NH4+-MONTMORILLONITES

Abstract: Reaction of hydroxy-A1 oligocations with Ce 3+- and La3+-exchanged montmorillonites, 1.25, 1.60, or 2.0 mmole A1/g smectite, yielded partially pillared hydroxy-A1 montmorillonite products containing a significant concentration of residual Ce 3+ or La 3+. After heat treatment at 250~ these products showed high surface areas (~340-500 mVg) and high basal X-ray powder diffraction spacings (18.0-18.6 /~). Calcination at 400~176 resulted in lower surface areas of ~200-450 m2/g and basal spacings of 16.3-18.3 A, the values showing a gradual decrease with a decrease in the A1/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-A1 oligomeric solution at 95 ~ 100~ instead of conventional aging for 2-3 weeks at 25~ Fluorinated NH4+-montmorillonites, containing 0.4 to 2.1 wt. % F, were prepared by reaction ofNH4 § montmorillonite at 600C with 1.0 to 3.0 N aqueous solutions of NH4F. Interaction of the fluorinated montmorillonites with hydroxy-A1 oligocations, using a ratio of 2.0 mmole A1/g smectite, yielded a series of cross'linked fluorinated montmorillonites with basal spacings of 17.9-18.0/~ and surface areas of 180- 325 m2/g after heat treatment at 250~ Calcination at 400~176 resulted in lower d(001) (16.6-17.7 /~) 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, Ad(001), of 9-10 A. Calculated lateral (interpillar) distances were in good agreement with the pore-size distributions determined in independent adsorption studies.

Feldspar Weathering in Lateritic Saprolite

Abstract: Feldspars in granitic saprolite in southwestern Australia have altered to halloysite, kaolinite, and gibbsite with no evidence of noncrystalline material. The secondary minerals are commonly present as intimate mixtures within altered feldspar grains, but discrete zones of gibbsite or halloysite-kaolinite also are present. Variations in the chemical microenvironment within micrometer-size zones in grains apparently controlled the type and distribution of secondary minerals. The alteration of both plagioclase and alkali feldspars involved congruent dissolution by soil solution and crystallization of halloysite, kaolinite, and gibbsite from this solution. Highly altered feldspar grains consist of etched feldspar fragments embedded within a highly porous framework of subhedral to euhedral platy crystals of kaolinite and gibbsite, or of spherical and felted aggregates of halloysite.

Role of structural hydrogen in the reduction and reoxidation of iron in nontronite

Abstract: The effects of reduction and reoxidation of octahedral Fe 3+ on the exchange of structural hydrogen in nontronite were determined using tritium (all) as a label element. The uptake of H from the surrounding solution of nontronite suspensions increased as the reduction of structural Fe 3+ increased. Similarly, the loss of H from the structure increased as the reduction increased. The results are generally consistent with a reduction mechanism involving the loss of structural OH, leaving the affected Fe sites with less than six-fold coordination. The attenuation of increased negative charge on the clay layer, however, was less than predicted by such a mechanism. During the reoxidation of reduced nontronite in suspension, about one-third of the H remaining as part of the structure following reduction was lost, whereas twice that amount of H was incorporated into the structure from the surrounding solution. A reoxidation mechanism is proposed whereby H20 from the surrounding solution is incorporated into the mineral structure followed by the elimination of a hydrogen ion, returning the Fe to six-fold coordination. This mechanism implies the reversibility of Fe reduction in nontronite.

Interpretation of Solid State 13C and 29Si Nuclear Magnetic Resonance Spectra of Kaolinite Intercalates

Abstract: 13C and 29Si nuclear magnetic resonance spectroscopy with magic-angle spinning bas been used to study the short-range ordering and bonding in the structures of intercalates of kaolinite with formamide, hydrazine, dimethyl sulfoxide (DMSO), and pyridine-N-oxide (PNO). The 29Si chemical shift indicated decreasing levels of bonding interaction between the silicate layer and the intercalate in the order: kaolinite: formamide (δ) = -91.9, ppm relative to tetramethylsilane), kaolinite: hydrazine (-92.0), kaolinite: DMSO (-93.1). The 29Si signal of the kaolinite:PNO intercalate (-92.1) was unexpectedly deshielded, possibly due to the aromatic nature of PNO. The degree of three-dimensional ordering of the structures was inferred from the 29Si signal width, with the kaolinite: DMSO intercalate displaying the greatest ordering and kaolinite: hydrazine the least. 13C resonances of intercalating organic molecules were shifted downfield by as much as 3 ppm in response to increased hydrogen bonding after intercalation, and in the kaolinite: DMSO intercalate the two methyl-carbon chemical environments were non-equivalent (δ = 43.7 and 42.5).

Palygorskite and sepiolite alteration to smectite under alkaline conditions

Abstract: The instability of palygorskite and sepiolite under soil conditions was investigated to determine if these fibrous minerals transform directly to smectite under laboratory conditions. The treatment of 100 mg (0.12 mmole) of palygorskite with 1 mmole of NaOH solution (17 ml) at 150~ for 24 hr yielded a smectite. Analcime and smectite were formed when -> 3 mmole of NaOH was used. The addition of - 8 mmole NaOH, sepiolite altered to an X-ray amorphous material. In the presence of A1 and Si, however, it transformed to smectite and analcime. Transmission electron microscopy, cation-exchange capacity, and X-ray powder diffraction studies of the products suggest that alteration was (1) via solution, or (2) by a structural reorganization wherein the basic 2:1 silicate structural units were unchanged. Key Wards--Alteration, Analcime, Cation-exchange capacity, Palygorskite, Sepiolite, Smectite, Sodium hydroxide.

Structure refinement of deuterated boehmite

Abstract: The crystal structure of a deuterated synthetic boehmite powder, γ-AIOOD, has been determined by time-of-flight neutron diffraction and Rietveld profile refinement in space group Cmcm to a weighted profile R of 3.71%. Cell dimensions are a = 2.868(1), b = 12.2336(4), and C = 3.6923(1) A. Alternate space groups for the boehmite structure suggested in the recent literature were found to be unacceptable. Atom positions, bond distances, and angles, with the exception of those involving hydrogen, were nearly identical to those determined by R. J. Hill in 1981 who studied a single crystal of boehmite by X-ray diffraction. All atoms were refined with anisotropic thermal parameters. The b value is 0.013 A larger, and the thermal ellipsoids of oxygen are slightly more anisotropic than those reported by Hill and may reflect the different samples studied.

Dehydration of Synthetic Hydrated Kaolinites: A Model for the Dehydration of Halloysite(10Å)

Abstract: Several hydrates can be synthesized from well-crystallized kaolinites; of importance to the present work are a 10-Zk hydrate (called the QS-10 hydrate), an 8.6-~k hydrate, and two kinds of partially dehydrated mixed-layer hydrates. One kind is a series of unstable materials with d(001) varying contin- uously between 10 and 8.6/~, and the other kind is stable with d(001) approximately centered at 7.9 ~t. The 10- and 7.9-7t phases have been observed in haUoysites by many workers using X-ray powder diffraction, and the 8.6-)i phase has been seen by others in selected area electron diffraction photographs. Infrared spectra reveal additional similarities between the synthetic hydrates and both halloysite(1071) and partially dehydrated halloysites. Because of these similarities, the synthetic hydrates can be used to develop a model for the dehydration of halloysite(10,/t). Previous work on the 10- and 8.6-/~1 hydrates identified two structural environments for the interlayer water. In one, the water is keyed into the ditrigonal holes of the silicate layer (hole water), and in the other, the water is more mobile (associated water). Both types are found in the QS-10 hydrate and halloysite(10,3i), whereas only hole water occurs in the 8.6-,/t hydrate. In the QS-10 hydrate, stronger hydrogen bonding between hole water and the clay makes the hole water more stable than the associated water. This difference in stability is responsible for a two-step dehydration process. The first step is the loss of associated water which results in a material with d(001) = 8.6 ~. This stable hydrate must be heated to temperatures near 200"C to drive off the remaining hole water. The less perfect structure of halloysite and its common curvilinear morphology reduce the difference in stability between hole and associated water molecules, so that when halloysite(10/~t) dehydrates, loss of hole water and associated water overlaps, and the d-spacing goes directly to 7.2-7.9 ~t.

Swelling pressure calculated from mineralogical properties of a jurassic opalinum shale, switzerland

Abstract: 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/ram 2. 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 x 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/~) 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 spec- imens are not available for direct measurement.

Effect of ion-pair formation on boron adsorption by kaolinite

Abstract: Boron adsorption on 2-0.2-#m size fractions of kaolinite at 25 ~ --- 2~ at pH values between 6.0 and 10.5 was studied. The kaolinite sample was pretreated to remove any surface oxide and hydroxide coatings. The initial concentrations of boron in solution ranged between 2 and 10 mg/liter with either KC104 or Ca(C104)2 as background electrolyte at constant ionic strength of 0.09 _+ 0.01 mole/liter. Boron speciation in equilibrium solutions was calculated by using the chemical equilibrium computer program GEOCHEM. The adsorption of boron on kaolinite in either medium showed similar dependence on pH and initial boron concentrations. Boron adsorption at higher pHs was noticeably higher in Ca(C104)2 medium as compared to KC104 medium. These differences were attributed to the formation and adsorption of CaB(OH4) + ion-pair species.

Dehydroxylation, rehydroxylation, and stability of kaolinite

Abstract: From hydrothermal experiments three pressure-temperature-time curves have been refined for the system A1EOa-SiOE-HEO and reversal temperatures established for two of the principal reactions involving kaolinite. The temperatures of three isobaric invariant points enable the Gibbs free energy of formation of diaspore and pyrophyllite to be refined and the stability field of kaolinite to be calculated. The maximal temperature of stable kaolinite decreases from 296~ at 2 kb water pressure to 2840C at water's liquid/vapor pressure, and decreases rapidly at lower pressures. On an isobaric plot of (H4SiO4) vs. ~ kaolinite has a wedge-shaped stability field which broadens toward lower temperature to include much of the (H4SiO4) range of near-surface environments. If (H4SiO4) is above kaolinite's stability field and the temperature is <100~ halloysite forms rather than pyrophyllite, an uncommon pedogenic mineral. Pyrophyllite forms readily instead of kaolinite above 1500C if(H4SiO4) is controlled by cristobalite or noncrystalline silica. Kaolinite and a common precursor, halloysite, are characteristic products of weathering and hydro- thermal alteration. In sediments, relatively little halloysite has survived due to its low dehydration temperature and instability at low water pressure, but kaolinite commonly has survived since the Devonian Period. In btLried sediments, the water pressure and (H4SiO4) requisite for stable kaolinite generally are maintained. In oxidized sediments and in pyritic reduced sediments, kaolinite commonly has survived, but where alkalies, alkaline earths, or aqueous iron has concentrated in the pore fluid, kaolinite has tended to transform to illite, zeolites, berthierine, or other minerals.

Distribution and Origin of Analcime in Marginal Lacustrine Mudstones of the Green River Formation, South-Central Uinta Basin, Utah

Abstract: X-Ray powder diffraction and thin section analyses indicate that marginal lacustrine mudstones of the Green River Formation in the south-central Uinta basin, Utah, contain abundant analcime. The analcime has a low Si/Al ratio (<2.31) and occurs as very fine grained disseminated crystals and, to a lesser extent, as coarser-grained pore-filling cement. Analcime-rich mudstones and associated sandstones, siltstones, and carbonates lack volcanic detritus and zeolites other than analcime, thus making it difficult to support the concept that the analcime formed from precursor zeolites derived from volcanic glass altered in saline, alkaline-lake water. Abundant dolomite, syneresis cracks, and the absence of freshwater pelecypods and gastropods suggest that the lake (Lake Uinta) was moderately saline and alkaline. The restricted illite-illite/smectite clay mineral suite in the analcime-rich mudstones suggests that detrital clays significantly altered in a moderately saline and alkaline environment, thereby providing a source of Si and Al for the formation of analcime. Red mudstones contain twice as much analcime as green mudstones (14 vs. 7 wt. %). Green mudstones have a day mineral suite consisting of illite (44 wt. %), mixed-layer illite/smectite (35 wt. %), smectite (12 wt. %), and minor kaolinite (4 wt. %) and chlorite (5 wt. %), whereas red mudstones have a more restricted day mineral suite consisting ofillite (68 wt. %) and mixed-layer illite/smectite (26 wt. %) with very minor smectite, chlorite, and kaolinite. Periodic minor fluctuations in lake level probably exposed large areas of shallow lacustrine-interdistributary green mud. Evaporative pumping on the exposed mudflats concentrated the moderately saline and alkaline-lake water, thereby producing Na-rich brines that enhanced the formation of analcime by accelerating the alteration of detrital clays and, perhaps, other minerals. Oxidation of iron from altered iron-bearing minerals stained the analcime-rich mud red with iron hydroxide or oxide (perhaps hematite). The overall reaction from green to red mud (mudstones) was probably: detrital phyllosilicates + Na-brine + iron-bearing minerals + oxygen → analcime + iron hydroxide or iron oxide.

Iron Sites in Nontronite and the Effect of Interlayer Cations From Mössbauer Spectra

Abstract: The 57Fe M~Sssbauer spectra of untreated, Ca- and K-saturated nontronite from Garfield, Washington, were measured. The spectrum of the untreated sample was computer-fitted to 8 peaks defining two octahedral, a tetrahedral, and an interlayer Fe3+-quadrupole-split doublets. In the Ca- and K-saturated samples interlayer Fe was absent. Spectra of the untreated sample were recorded at increasing increments of background counts from 2.8 x l0 s to 9.2 x 106. An evaluation of the initial 4- and 6-peak models and the acceptable 8-peak model, computer-fitted to each spectrum, shows that if the X 2 value is used as a measure of the goodness of the fit, the spectra should be recorded to a background count greater than 3 x 106. The resulting x 2 value then reflects both the validity of the model used and the extent of disorder within the structure. The x 2 value depends linearly on the background counts obtained. A comparison of the spectra of the Ca- and K-saturated samples with that of the untreated sample shows that the interlayer cations exert a considerable influence on the individual component resonances, particularly the outer octahedral doublet. Hence, it is likely that electrostatic interactions of the nearby tetrahedral Fe 3 + and the interlayer cations give rise to two distinct electric field gradients within neighboring cis-(FeO4(OH)2) sites, and hence two octahedral Fe 3+ doublets in the MiSssbauer spectrum. These results are consistent with earlier electron diffraction data in the literature.

Effect of clay mineralogy and aluminum and iron oxides on the hydraulic conductivity of clay-sand mixtures

Abstract: Changes in hydraulic conductivity and clay dispersivity of clay-sand mixtures (four reference smectites and Fithian illite) as a function of concentration (0.01 M Cl− and distilled water) and sodium adsorption ratio (SAR ≤ 30) of the percolating solution were measured. In addition, the effect of sand percentage, sand particle size, and addition of AlCl3 and FeCl3 on the hydraulic conductivity of the mixtures were measured. Clay dispersion and migration out of the 3% clay columns was substantial. The clay dispersed only in the distilled water system; dispersion increased with an increase in the percentage of exchangeable Na and was about the same for the Wyoming montmorillonite and Fithian illite. Conversely, the clay swelled in the 0.01 M Cl− solution. The swelling of the montmorillonites increased in the order: Upton, Wyoming = Belle Fourche, South Dakota > Polkville, Mississippi > Otay, California, and was higher than that of the Fithian illite. The swelling and dispersion of the clay accounted for the changes in hydraulic conductivity. Mixtures treated with FeCl3 and AlCl3 were leached with NaCl-CaCl2 solutions until the pH of the effluent exceeded 6.5. The composition of the exchangeable phase was then determined by the SAR of the leach solutions. At pH > 6.5, the polycations hydrolyzed and were present as the hydroxy-polymer species. The hydraulic conductivity of the mixtures decreased as exchangeable Na increased, but the decrease was less than in untreated mixtures, AlCl3 was more effective in maintaining hydraulic conductivity than FeCl3. In montmorillonite clay with an ESP of 20, less than 5% of a complete Al-interlayer was enough to prevent a reduction in hydraulic conductivity. Packets in the day systems tested explain the high efficiency of the Fe and Al polycations.

Size distribution of allophane unit particles in aqueous suspensions

Abstract: 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 A 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 A. 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.

Effect of Simple Sugars on the Alkaline Transformation of Ferrihydrite into Goethite and Hematite

Abstract: The transformation of ferrihydrite to goethite and hematite in the pH range 9–13 is retarded by the presence of simple sugars (>- 10-4 M concentration). The retarding effect is related to the extent of adsorption of the sugar on ferrihydrite. Maltose and glucose adsorb strongly and inhibit the transformation by preventing both aggregation and dissolution of the ferrihydrite. Sucrose adsorbs to a much lesser extent than the other sugars and appears to hinder the nucleation and growth of goethite in solution. Hematite formation relative to that of goethite is favored by the sugars in the order: maltose >glucose ≫ sucrose. Maltose and glucose cause hematite to grow as prismatic crystals rather than as hexagonal plates and also lead to a new type of twinned goethite; one with epitaxial outgrowths of goethite on a prismatic crystal of hematite. In alkaline media glucose and maltose are partly transformed into a mixture of different sugars and hydroxycarboxylic acids, and it is probable that modification of the hematite crystal shape is due to the presence of the degradation products rather than to the nature of the original sugar. The results of this work suggest that cyclic molecules influence the transformation of ferrihydrite to a lesser extent than do acyclic molecules.

Growth Conditions and Genesis of Spherical and Platy Kaolinite

Abstract: Spherical and platy kaolinite crystals were prepared under several hydrothermal conditions. Spherical kaolinite was produced mainly at high solid/water ratio (1/4) and at low temperatures (150°-200°C). Platy kaolinite predominated in products from experiments with intermediate solid/water ratios (1/256-1/16) and at high temperatures. Boehmite predominated at low solid/water ratios (1/4096) at all experimental temperatures (180°-220°C). The results indicate that the growth of the spherical kaolinite was favored at high degrees of supersaturation, whereas the growth of the platy kaolinite was favored at relatively low degrees of supersaturation.

Structure and Growth Mechanism of Glauconite as Seen by High-Resolution Transmission Electron Microscopy

Abstract: The internal fabric of glauconite pellets has been studied by high-resolution transmission electron microscopy (HRTEM) for a better understanding of the glauconitization process. Typical “lamellae” which make up the glauconite pellets showed a spindle-like arrangement of layered crystallite packets. Three main mineral phases were detected: (1) well-ordered glauconite sensu stricto (d(001) = 10 A) generally in the middle of the spindles; (2) a poorly ordered and undetermined layered-phase “X” with d(001) ~ 12.5 A, usually sandwiching glauconite such that the interface between the two materials is very sharp; and (3) a noncrystalline or gel-like phase located between the lamellae. A 14-o smectite-like phase was rarely observed at the periphery of some grains. The glauconite crystallites clearly showed characteristic growth features (e.g., growth steps), whereas the unknown phase X exhibited destabilization characteristics. A structural analysis of the pure glauconite indicates that this dioctahedral mica was present in the IMd (disordered), 1M, and, to a much lesser extent, 2M1 polytypic forms. HRTEM revealed no interlayering of glauconite with the other layered phases. Rather, it appeared to have formed by a layer-growth mechanism at the expense of the unknown phase X which apparently converted into non-crystalline matter before converting to glauconite. The precursor function of the interlamellae “gel” phase during the evolutive process of glauconitization is not understood.

Formation of highly selective cesium-exchange sites in montmorillonites

Abstract: Ion-exchange sites with very high selectivity for Cs (\(\Delta{\rm{G}}_{\rm{Ca}^{2+}}^{\rm{Cs}^{+}}\) = 40 kJ/eq) similar to illite were generated in a controlled way in montmorillonites b. (1) repeated wetting-drying cycles and b. (2) charge reduction using the Hofmann-Klemen effect. An almost continuous range of sites with selectivities varying from ln \({\rm{K}}_{\rm{Ca}^{2+}}^{\rm{Cs}^{+}}\) = 33 to 5 was observed.

Mechanism controlling the volume change behavior of kaolinite

Abstract: The possible physical and chemical forces controlling the volume change behavior of kaolinite [1318-74-7] were ascertained from the sediment volume of kaolinite in various solvents under no external load condition and from conventional oedometer measurements of kaolinite in several pore fluids. The minimum sediment volume of $14.5 cm^3/10 g$ clay occupied by kaolinite in water where repulsive (R) forces were dominant indicated that the R contribution was insignificant for kaolinite. The maximum sediment volume of $25.0 cm^3/10 g$ clay in $C_6H_6$, where coulombic attraction forces were significant, suggested that electrostatic attraction between silicate sheets and midplane cations and van der Waals forces were not appreciable for kaolinite. The positive edge-negative face bonding of kaolinite particles in $C_6H_6$ was unlikely. The $3688 cm^{-1}$ band in the IR spectrum of a kaolinite-dimethylamine sample decreased by $10 cm^{-1}$ on H-bond formation of the solvent molecule with the exposed structural hydroxyls of the octahedral sheet. The adsorbed solvent molecules likely H-bonded with an adjacent clay particle as indicated by the decrease in sediment volume with increase in dipole moment of the solvent molecule. In the oedometer tests with various pore fluids, a high void ratio of approximate 1.3 was obtained for kaolinite in n-heptane, and hexane (\mu \simeq 0) at an external pressure of $1 kg/cm^2$ probably because the weakly bonded kaolinite particles were randomly oriented. At the corresponding applied pressure, a lower void ratio of 0.88 resulted in water (\mu = 1.84) where the stronger H-bond between flat layer surfaces of adjacent particles favored a parallel orientation of clay particles. The volume change behavior was essentially controlled by frictional forces and clay fabric. In nonpolar solvents the random arrangement of kaolinite particles and the frictional forces mobilized a high shear resistance on the application of a consolidation pressure, resulting in a lower compressibility. In a solvent with high dipole moment the parallel array of clay particles mobilized less shear resistance and produced a greater compression.