Showing papers in "Clays and Clay Minerals in 1979"

The influence of aluminum on iron oxides; Part II, Preparation and properties of Al-substituted hematites

Abstract: Aluminum-substituted hematites (Fez-xAlxO3) were synthesized from Fe-A1 coprecipitates at pH 5.5, 7.0, and in 10 -1, 10 -2, and 10 -2 M KOH at 700C. As little as 1 mole % AI suppressed goethite completely at pH 7 whereas in KOH higher AI concentrations were necessary. AI substitution as determined chemically and by XRD line shift was related to AI addition up to a maximum of 16-17 mole %. The relationship between the crystallographic ao parameter and AI sub- stitution deviated from the Vegard rule. At low substitution crystallinity of the hematites was improved whereas higher substitution impeded crystal growth in the crystallographic z-direction as indicated by differential XRD line broadening. At still higher AI addition crystal growth was strongly retarded. The initial AI-Fe coprecipitate behaved differently from a mechanical mixture of the respective "'hydroxides" and was, therefore, considered an aluminous ferrihydrite.

High Surface Area Solids Obtained by Reaction of Montmorillonite with Zirconyl Chloride

Abstract: Exchange reactions of Na-montmorillonite with zirconyl chloride solutions give products with basal spacings near 18 A which are stable to 500~ and have surface areas of the order of 300-400 m2/g. The Na ions are exchanged with tetrameric hydroxy cations (Zr4(OH)I( nH~O) 2+. The high surface area is attributed to the porosity formed by stable zir- conium oxide" pillars" formed by dehydroxylatlon of the complex cation. The nitrogen adsorption isotherms are of Lang- muir type and are consistent with adsorption in interlayer micropores. Reduced-charge montmorillonites, formed by ap- plication of the Hofmann-Klemen procedure, give either similar or slightly smaller surface areas. was used. The same montmorillonite was used in a pre- vious study (Yamanaka and Brindley, 1978) where the chemical analysis and structural formula are given. Na- and Li-saturated samples were prepared by treatment with the respective 1 N chloride solutions, with sub- sequent washing by centrifugation and dialysis to re- move excess chloride.

Influence of Organic Anions on the Crystallization of Ferrihydrite

Abstract: Hydroxy-carboxylic acids inhibit the crystallization of ferrihydrite in the pH range 9–11 in the order $$citric >meso\,tartaric >L - tartaric \gg lactic$$ and favor hematite formation relative to goethite in the order $$L - tartaric >citric >meso\,tartaric >lactic.$$ The crystal shape of hematite can change from hexagonal plates to acicular in the presence of these acids. The influence of the acids on the crystallization rises with increasing concentration and with falling pH. The effectiveness in suppressing crystallization depends on whether and how strongly the acid adsorbs on ferrihydrite and how strongly it complexes with Fe3+ in solution. Inhibition of crystallization of hematite is believed to be due to the di- and tricarboxylic acid linking ferrihydrite particles in an immobile network. Goethite formation is suppressed by the acid complexing with Fe in solution and hindering nucleation; strongly adsorbing acids also adsorb on the nuclei and hinder further growth. Certain acids can induce hematite formation because they contain a group which acts as a template for nucleation of hematite.

Black shale - Its deposition and diagenesis.

Abstract: Black shale is a dark-colored mudrock containing organic matter that may have generated hy- drocarbons in the subsurface or that may yield hydrocarbons by pyrolysis. Many black shale units are enriched in metals severalfold above expected amounts in ordinary shale. Some black shale units have served as host rocks for syngenetic metal deposits. Black shales have formed throughout the Earth's history and in all parts of the world. This suggests that geologic processes and not geologic settings are the controlling factors in the accumulation of black shale. Geologic processes are those of deposition by which the raw materials of black shale are accumulated and those of diagenesis in response to increasing depth of burial. Depositional processes involve a range of relationships among such factors as organic productivity, clas- tic sedimentation rate, and the intensity of oxidation by which organic matter is destroyed. If enough or- ganic material is present to exhaust the oxygen in the environment, black shale results. Diagenetic processes involve chemical reactions controlled by the nature of the components and by the pressure and temperature regimens that continuing burial imposes. For a thickness of a few meters beneath the surface, sulfate is reduced and sulfide minerals may be deposited. Fermentation reactions in the next several hundred meters result in biogenic methane, followed successively at greater depths by decarbox- ylation reactions and thermal maturation that form additional hydrocarbons. Suites of newly formed min- erals are characteristic for each of the zones of diagenesis.

Origin of iron-rich montmorillonite from the manganese nodule belt of the North Equatorial Pacific

Abstract: Clay minerals in the upper 50 cm of sediment that surround the Cu- and Ni-rich manganese nodules in the North Equatorial Pacific form two fractions: terrigenous (mostly eolian) illite, chlorite, and kaolinite, and authigenic smectite. Smectite increases with depth in box cores from 26 to 39% and from 53 to 66% in the easternmost and westernmost areas respectively, and with distance seaward from the Americas from 26 to 53% in surface deposits. The change in the amount of smectite relative to other clay minerals is due to dilution by terrigenous debris; smectite probably forms at a uniform rate over much of the North Pacific deep-sea floor. The δO18 value for the smectite is +29.6‰ which suggests that it formed authigenically at a temperature characteristic of the deep-sea floor. The smectite is an Fe-rich montmorillonite that probably forms by the low-temperature chemical combination of Fe hydroxides and silica. Silica is derived from dissolution of biogenic debris, and the Fe hydroxide is from volcanic activity at the East Pacific Rise, 4000 to 5000 km to the east. Al in the authigenic montmorillonite may be derived from the dissolution of large amounts of biogenic silica or from river-derived Al that is adsorbed on Fe-Mn hydroxides in the oceans. The Fe-montmorillonite contains relatively abundant Cu, Zn, and Mn and is of possible economic importance as a source of these and other metals.

The crystal structure of boehmite

Abstract: The crystal structure of a synthetic boehmite sample has been refined to an R of 0.047 in the space group Amam from X-ray powder diffraction data. Inclusion of hydrogen atoms and/or refinement in the space group A21am gave poorer results. Cell dimensions were determined as a = 3.6936 (± 0.0003), b = 12.214 (± 0.001), c = 2.8679 (± 0.0003) A. All Al-O(OH) distances lie between 1.88 and 1.91 A. Shared octahedral edges are 2.51–2.52 A, and unshared octahedral edges are 2.86–2.87 A, in excellent agreement with those for layered silicates. The O-H … O distance between contiguous octahedral sheets is 2.71 A. The computed X-ray pattern matches closely with the experimental pattern, indicating the degree to which the crystal structure has been determined.

The Influence of Aluminum on the Formation of Iron Oxides. IV. The Influence of [Al], [OH], and Temperature

Abstract: Ferrihydrite was transformed to goethite and/or hematite at various temperatures, (OH), and IAl). Increasing temperature and (AI) favored hematite, increasing (OH) favored goethite. A given (AI) induces hematite more effectively at lower (OH). AI substitution in goethites increased linearly with log(All, but was independent of temperature. At a givea (All, substitution increased with decreasing (OH). In a plot of AI/Fe in the goethite against (AI)/(Fe(OH)C) in solution a straight line was obtained for all preparations independent of (OH).

Infrared and mossbauer studies of reduced nontronites

Abstract: lnfrar ed and M6ssbauer spectroscopy show that the extent of the reduction of nontronite is dependent on the chemical composition of the nontronite and on the nature of the reducing agent. Hydrazine reversibly reduces about 10% of the iron in all of the nontronltes studied irrespective of composition and it is suggested that the resulting ferrous iron occurs only in distorted octahedral sites. Similar conclusions are reached for the dithionite reduction of the nontronites containing little tetrahedral iron, but for those with more than one in eight silicons replaced by iron, changes brought about by dithionite treatment are irreversible due to dissolution of appreciable quantities of iron. Results from both spectroscopic techniques suggest that iron in tetrahedral sites is preferentially dissolved and that up to 80% of the structural iron can be reduced. Evidence is presented for the formation in these extensively reduced nontronltes of a small amount of a mica-like phase resembling celadonite or glauconite, and, as dithionlte is used for the pretreatment of soils, the implication of this obser- vation is briefly discussed. The use of deuterated hydrazine as a reducing agent has enabled the nontronite absorption band near 850 cm -1 to be assigned to a Si-O (apical) stretching vibration, which is inactive in the infrared for perfect hexagonal symmetry, but which is activated by distortions in the tetrahedral layer.

Neutron diffraction from clay-water systems

Abstract: The use of neutron diffraction to determine some of the structural properties of montmorillonite-water systems at low water concentrations is described. The samples were prepared by compression or suction to give clay samples with between one and three molecular layers of water between the plates. About 10% of the platelets in the clay are randomly oriented. The remainder are partially oriented in the plane of the sample, with an angular spread of 40° about the mean orientation. It is suggested that these oriented domains are formed from the larger platelets present in the system. The Bragg diffraction pattern is better explained by a disordered lattice model rather than by a mixture model with small particles having a well-defined lattice spacing. We have fitted both the intensities of (00l) reflections and the shape of the (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value. The half width of the spread is about 10% of the lattice spacing. No significant structural differences are found between Li, Na, K, and Cs montmorillonites. The method of preparation has no effect on the structural properties of the large platelet particles but does affect the randomly oriented fraction. The lattice spacing of the latter appears to be better defined for samples prepared by compression. Experiments on the variation of lattice spacing with humidity indicate that the structural model we have used is adequate except at humidities where the system is changing over from one to two, or two to three water layers.

Role of iron reduction in the conversion of smectite to illite in bentonites in the disturbed belt, montana

Abstract: Abstraet--Cretaceous bentonites were collected in outcrop from the Sweetgrass Arch and the Disturbed Belt in Montana. The mixed-layer illite-smectite (I/S) components of the bentonites from the Sweetgrass Arch have from 0 to 25% illite layers and no detectable structural Fe 2+, whereas the samples from the Disturbed Belt have from about 25 to 90% illite layers, and all contain Fe 2+. A positive correlation (r = 0.89) exists between the percentage of structural iron that is Fe z+ and the amount of fixed interlayer K in the US. The higher percentage of illite layers in the samples from the Disturbed Belt is attributed to reactions related to elevated temperatures caused by burial beneath thrust sheets. The increase in Fe2+/Fe 3+ with increasing percentages of illite layers is tentatively attributed to a redox reaction involving the oxidation of organic matter. Although there is no statistical evidence for an increase in octahedral charge with an increase in illite layers when all the samples are considered together, iron reduction may have contributed as much as 10 to 30% of the increase in total structural-charge that occurred in any given sample during metamorphism. The remaining structural charge increase can be attributed to the substitution of Al 3+ for Si 4§ in the tetrahedral sites.

Biotite alteration in deeply weathered granite; I, Morphological, mineralogical, and chemical properties

Abstract: Biotite in deeply weathered granitic rocks in southwestern Australia has altered to exfoliated grains composed of biotite, mixed-layer clay minerals, kaolinite, vermiculite, gibbsite, goethite, and hematite. Discrete vermiculite and vermiculite-dominant mixed-layer clay minerals are not major weathering products. Oxidation of octahedral iron in biotite is associated with ejection of octahedral cations, loss of interlayer K, and a contraction of the b-dimension of the biotite sheet. Si, Mg, Ca, Mn, K, and Na are lost from biotite during weathering, and Ti, Al, Ni, and Cr are retained. Fe and water have been added to the grains during weathering. Much Fe occurs as aggregates of microcystalline, aluminum-rich goethite particles on flake surfaces and within etchpits, with smaller amounts occurring as hexagonal arrangements of lath-shaped crystals of goethite on flake surfaces.

The “Layer Charge” of Regular Interstratified 2:1 Clay Minerals

Abstract: Alkylammonium ion exchange on mixed-layer minerals gives detailed information about the variation of cation density in succeeding interlayer spaces. Three mixed layer samples from Japan (supplied by Dr. H. Kodama) were in- vestigated. Their nearly 1:1 interstratification is based on regularly alternating high- and low-charged interlayer spaces, which are caused by a regular sequence of polar layers. The cation density in the high-charged interlayer spaces is >0.8 eq/(Si, Al)4Oto. The low-charged interlayer spaces have an average cation density of 0.4 eq/(Si, Al)4Oio and heterogeneous charge distribution. The kind of heterogeneity of the Goto Mine sample differs from that of the Yonago Mine and the Honami Mine samples. The Goto Mine specimen has a rather regular sequence of the low- and high-charged interlayers in proportions close to 0.50:0.50. The other two samples contain interlayer spaces with pronounced unsymmetrical charge distribution. The Yonago Mine sample probably has in random distribution with the polar layers about 10% mica-like layers segregated to packets of three and more layers; the ratio of high-charged interlayers to the low-charged ones is increased to about 0.55:0.45. The Honami Mine sample probably contains isolated mica-like layers or pairs of them. The proportion of the high-charged interlayers is estimated to be about 0.53:0.47 and is lower than determined by Kodama from the glycerolated sample. The samples investigated may be considered as end-members of a series of interstratified specimens which begins with smectites with mixed-layer like charge distribution.

Synthesis and Properties of Heat-Stable Expanded Smectite and Vermiculite1

Abstract: When aqueous dispersions of Na+-smectite or n-butylammonium-vermiculite react with sulfate salts of Fe(II), Co(II), or Ni(II) bipyridyl or 1, 10-phenanthroline complexes in excess of the cation-exchange capacities, intersalated phases with spacings of about 29.5 A are obtained. Thermal decomposition of the intersalated complex cations affords expanded phases with a d(001) spacing near 18 A for the smectites and near 28 A for the vermiculites. These phases are stable to temperatures of at least 550°C. Nitrogen surface areas of the fired products are as high as 400 m2/g.

Hydroxyl orientations in 2:1 phyllosilicates

Abstract: The hydroxyl orientations in 31 dioctahedral and trioctahedral 2:1 phyllosilicate structures have been determined by electrostatic energy calculations. These structures included micas, brittle micas, and other related minerals exhibiting ordered as well as disordered cation distributions. The dioctahedral micas and brittle micas were examined with and without the interlayer cation. A range of orientations from 1.3 o to 183.3 ~ (the angle p between the O-H and (001) measured with respect to the M1 site) were found. The orientations for the dioctahedral structures represent a continuum of values whereas the trioctahedral species exhibit two possible orientations separated by an energy barrier. One orientation is near 90~ the other is near 180 ~ The latter orientation results from a concentration of charge on the interlayer (IC) and tetrahedral (T) sites at the expense of the octahedral (M) sites. A multiple regression analysis of all 31 structures, using as predictors the a and b cell parameters, d0ol, and the charges for T, IC, M1, and M2 sites, was performed. This analysis indicated that the important factors are the charges for IC, T, and M2 sites. When treated as a separate group, one finds the same factors for the dioctahedral structures. The trioctahedral orientations are determined by the charge on the M2 site and the amount of tetrahedral ro- tation. Using these two predictor equations, the value of p can be estimated with a standard deviation of 4.7 ~ and 2.9 ~ for the dioctahedral and trioctahedral cases, respectively.

A Method for the Quantitative Estimation of Clay Minerals in North Pacific Deep-Sea Sediments

Abstract: The addition of a 10% talc internal standard to North Pacific sediments allows the relative abundances of clay minerals to be determined both accurately and precisely by X-ray powder diffractometry. Linear programming can be used to generate factors for converting talc-normalized peak areas to weight percentages; hence, absolute clay-mineral abundances can be estimated. This procedure minimizes residuals (nondiffracting or poorly crystalline components), but its accuracy is untested. Even this procedure results in an average residual of almost 30% for North Pacific sediments; other peak-area to weight conversion schemes generate even larger values. In general, there is no correlation between clay-mineral abundances estimated from talc-normalized peak areas and abundances derived from the assumption that the sum of smectite, illite, kaolinite, and chlorite is 100%. This accounts for the past difficulties in relating bulk-sediment chemistry to clay mineralogy.

Water vapor isotherms and heat of immersion of Na/Ca-montmorillonite systems; II, Mixed systems

Abstract: Abst~et--Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of mixed Na/Ca-montmorillonite were measured at 250C at various RH. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. It was concluded that the electrostatic forces between the adsorbed cations and the water molecules are the dominant forces in the hydration of the clay. Thus, at low moisture content, only the adsorbed Ca-ions are hydrated. The heat released when Na-platelets condense to form Ca-packets was measured, and it was suggested that this energy term is the driving force for the demixing phenomena.

Effect of ionic strength and ion pair formation on the adsorption of nickel by kaolinite

Abstract: Adsorption of Ni(II) by Ca- and Na-saturated kaolinites was studied in equilibrating solutions with total Ni concentrations ranging from 118 to 946 μg/liter. Background electrolytes used in these experiments were 0.005,0.01,0.025, and 0.5 M Ca(N03)2,0.002 and 0.005 M CaSO4, 0.01 and 0.1 M NaNO3, and 0.005 and 0.05 M Na2SO4, Ion speciation in equilibrium solutions was calculated by the computer program GEOCHEM. Computed Ni2+ concentrations and activities at equilibrium were correlated with total Ni adsorbed by kaolinite. Increasing ionic strength resulted in decreasing Ni adsorption. Adsorption of Ni was greater from solutions when NO3 was the dominant anion. Based on adsorption data in SO4 medium, the standard free energy of adsorption of Ni2+ ion on kaolinite was computed to be —27 kJ/mole. Die Adsorption von Ni2+ durch Ca- und Na-gesattigte Kaolinite wurde in Losungen nahe dem Gleichgewicht untersucht, die Gesamt-Ni-Konzentrationen im Bereich von 118 bis 946 μ.g/liter hatten. Als Hilfselektrolyte wurden in diesen Experimenten verwendet: 0,005, 0,01, 0,025, und 0,5 M Ca(NO3)2, 0,002 und 0,005 M CaSO4, 0,01 und 0,1 M NaNO3 sowie 0,005 und 0,05 M Na2SO4. Die Verteilung der Ionenarten in den Gleichgewichtslosungen wurde mit dem Computerprogramm GEOCHEM berechnet. Die berechneten Ni2+-Konzentrationen und -Aktivitaten bei Gleichgewicht wurden mit dem Gesamt-Ni, das durch Kaolinit adsorbiert war, korreliert. Eine zunehmende Ionenstarke bewirkt eine abnehmende Ni-Adsorption. Die Ni-Adsorption aus den Losungen war groser, wenn NO3− das vorherrschende Anion war. Aufgrund der Adsorptionsdaten bei SO42−-Medium wurde die Freie Energie der Ni2+-Adsorption an Kaolinit mit —27 kj/mol berechnet. L’adsorption de Ni(II) par des kaolinites saturees de Ca et Na a ete etudiee dans des solutions equilibrantes avec des concentrations totales de Ni s’etendant de 118 a 946 μg/litre. Des electrolytes de fond utilisees dans ces experiences etaient 0,005, 0,01, 0,025, et 0,5 M Ca(N03)2; 0,002 et 0,005 M CaSO4; 0,01 et 0,1 M NaNO3; et 0,005 et 0,05 M Na2SO4. La speciation d’ions dans les solutions d’equilibre a ete calculee par le programme d’ordinateur GEOCHEM. Les concentrations et activites de Ni2+ calculees a l’equilibre ont ete apparentees a Ni total adsorbe par la kaolinite. La force ionique croissante a resulte en une adsorption decroissante de Ni. Lorsque NO3 etait l’anion dominant dans les solutions, l’adsorption de Ni etait la plus elevee. En se basant sur les donnees d’adsorption dans un milieu SO4, on a calcule que l’energie libre standard d’adsorption de l’ion Ni2+ sur la kaolinite etait —27 kJ/mole.

Layer charge--cation-exchange capacity relationships in montmorillonite

Abstract: The charge density distribution among different classes of a series of reduced charge mont-morillonites is heterogeneous as in the parent Camp Berteau clay. In addition, charge reduction proceeds inhomogeneously. Up to 20% differences in charge density can be accounted for by aikyl chains extending at the edges of the clay particle. A realistic charge density-cation-exchange capacity relationship for hec-torite, Otay montmorillonite, and a series of reduced charge montmorillonites of Camp Berteau is obtained by accounting for the influence of particle radius and for the extent of alkyl chains lying outside the clay layers in the charge density calculations.

The Hydrothermal Transformation of Sepiolite to Stevensite and the Effect of Added Chlorides and Hydroxides

Abstract: Hydrothermal reactions in the system sepiolite/H2O have been examined between 149° and 316°C. Approximately 10–20% of the starting sepiolite was converted to a smectite (stevensite) at 204°C within 24 hr. Similar results were obtained when CaCl2, NaOH, Ca(OH)2, or Mg(OH)2 was added to the system. In the presence of NaCl, about 60% of the sepiolite was converted to stevensite, whereas, only 5% stevensite formed in the presence of MgCl2. Greater amounts of stevensite formed at 260°C in these systems. Above 316°C, 60–80% of the sepiolite was converted to stevensite in 24 hr, regardless of the presence or absence of salts. Within the experimental conditions used, temperature is the most important factor in the sepiolite-to-stevensite conversion. At or below 216°C, sepiolite appears to transform into stevensite by dislocations involving c12 glides that are triggered by the stresses of the hydrothermal conditions. Above this temperature, stevensite seems to form by direct precipitation after dissolution of sepiolite.

Aluminum-Bearing Goethite in Venezuelan Laterites

Abstract: The presence of Al-bearing goethites has been unequivocally established in Venezuelan laterite sediments by means of infrared spectroscopy (IR), chemical dissolution, and X-ray powder diffraction (XRD) methods. The composition of these samples ranges from (Fe0.agA10,11)O(OH) to (Fe0.r~A10.24)O(OH). The data of dissolution experiments using a modified dithionite (CDB) treatment suggest a parallel behavior between Fe and A1; the gradual dissolution of A1 is associated with the destruction of the Al-containing goethite. The interpretation of the CDB dissolution results for SiO~/Fe2Oz is different; silica was only slight- ly extracted from phases other than goethite. Substitution of Fe a§ by AP + in these goethites was represented on the XRD patterns by a lowering of the (110) and (111) reflections corresponding to a reduction in size of the unit cell of goethite. IR spectroscopy showed the formation of such solid solutions by a shift of the 405 cm -1 absorption band, assigned to v (Fe-O) in synthetic goethite, to >460 cm -~ in the spectrum of AI- bearing natural goethite. Moreover, this spectrum shows a shift of the 3140 cm -~ absorption, due to v (OH), to higher frequencies, indicating a H-bond weakening in (FexA1c~_~)O(OH) compared to FeO(Ot-I).

Surface Reactions of Parathion on Clays1

Abstract: The adsorption-catalyzed degradation of parathion on clay surfaces is a hydrolysis process, proceeding either directly or through a rearrangement step. The rate and mechanism of degradation are dependent on the nature of the clay, its hydration status, and saturating cation. A mechanism for parathion degradation at adsorption sites on clay surfaces, in the absence of a liquid phase, is proposed.

The Interaction Between Roundup (Glyphosate) and Montmorillonite. Part I. Infrared Study of the Sorption of Glyphosate by Montmorillonite

Abstract: The reaction between the herbicide "Roundup," (PAH)3G, which is the commercial name of the iso-pro- pylammonium salt of glyphosate (HsG, N-phosphonomethyl glycine), and montmorillonite was studied. The adsorption of the anionic component of Roundup glyphosate anion, G -s, from an ethanol solution is achieved by repeated immersion of the clay film in the alcohol solution followed by drying for 6-12 hr after each immersion. During the adsorption process the surface acidity of the interlayer space must be sufficiently high to protonate the anion. A zwinerion glyphosate is thereby formed in the interlayer space. Association forms are obtained in the interlayer space in which the COOH and the POsI-I groups are linked to the exchangeable cations through water bridges. Adsorption of the glyphosate anion from aqueous solution of Roundup occurs when this anion forms a neutrally or positively charged complex with the exchange- able cation. This may occur with AI- and Fe-montmorillonite, when the molar ratio glyphosate:metal is such that a complex with a 1: I ratio can be formed in the interlayer space. To clarify the reaction mechanism, adsorption of glycine by mont- moriUonite from ethanol solution was also studied. The associations obtained between glyphosate and exchangeable cat- ions are less variable than those obtained between glycine and exchangeable cations in the interlayer space of montmoril- lonite. The following species of adsorbed glycine were identified: glycinium cation, zwinerion glycine, glycine complexed with metal cations either as a monodentate or as a bidentate ligand. In the latter case a chelate is formed.

Ideal Behavior in Na+-Trace Metal Cation Exchange on Camp Berteau Montmorillonite

Abstract: The conditions under which an exchanger phase will behave as an ideal mixture are established from thermodynamic principles. It is shown that, if a stoichiometric cation-exchange reaction is reversible, the exchanger phase will exhibit ideal behavior if the Vanselow selectivity coefficient is independent of the exchanger composition. This criterion is applied to some recently published data for Na+-trace metal cation exchange on Camp Berteau montmorillonite. An analysis of the data suggests that, so long as the exchange process is reversible, Na+-trace metal cation exchange produces an exchanger phase that behaves as an ideal mixture.

Mobility and Reactions of VO2+ on Hydrated Smectite Surfaces1

Abstract: The electron spin resonance (ESR) spectra of varying quantities of vanadyl ion (VO2+) adsorbed on hydrated hectorite indicated that hydrolysis of VO2+ was promoted at low levels of adsorption. The hydrolyzed product was adsorbed on the clay surfaces, with a ligand environment that was partially aqueous and partially hydroxide in nature. Greater amounts of VO2+ adsorbed on wetted hectorite obscured the ESR spectrum of the strongly adsorbed hydrolysis product with a solutionlike spectrum. An approximately 50% reduction in rotational mobility of VO2+ relative to solution was indicated by the linewidth of this spectrum. Loss in mobility occurred with reduction of the interlamellar spacing until, under strongly dehydrating conditions, the VO(H2O)52+ ions became aligned with the V=O bond axis normal to the plane of the clay platelets.

A mossbauer investigation of glauconite and its geological significance

Abstract: Ahstraet--M6ssbauer spectra of 9 glauconite samples from Upper Cretaceous and Lower Tertiary strata in the South Island of New Zealand contain a broad shoulder due to low intensity absorption continuous between 1.0 and 2.5 mm/sec when the absorber is at room temperature; the shoulder is absent, and sharp peaks are apparent in spectra taken with the absorber at 80~ The data suggest that electron transfer occurs between adjacent Fe 3+ and Fe z+ ions at room temperature. The low temperature spectra indicate that all Fe in the glauconites is in octahedral coordination. Fe z+ and Fe z+ ions occur in both cis and trans sites; Fe z+ shows a strong preference for cis sites whereas Fe 2+ shows an even stronger preference for trans sites. The partially variable oxidation state of Fe in glauconite is interpreted in terms of a geochemical model for glauconitization of a degraded or incomplete progenitor phyllosilicate. The model involves exchange of Fe ~+ for other cations which temporarily stabilize the progenitor, followed by FeZ§ 3+ charge transfer reactions. Each reaction results from the system's tendency towards equilibrium. The model is supported by the observation that artificially leached glauconite increases both its Fe z+ and its Fe z+ content when placed in a solution containing Fe 2+ as the only Fe ion present.

Thermodynamic and structural features of water sorption in zeolites

Abstract: The water adsorption capacity of zeolites is a function of pressure and temperature. Desorption of zeolites may be of three types, wherein the crystal lattice undergoes (1) no or little change, (2) a reversible change, or (3) an irreversible change. In the first two cases, the divariance of the zeolite-water vapor equilibrium results in networks of isobars, isotherms, and isosteres which can be transformed into a “characteristic” curve following the Polanyi-Dubinin theory. Because the volume of the micropores of a zeolite structure is constant, the isotherms and “characteristic” curve can be transformed linearly. During desorption, if the volume of the micropores varies due to a change of structure, the curves show linearity breaks. On the basis of X-ray diffraction, differential thermal, and thermal gravimetric analyses, the equilibrium curves and structural changes of heulandite and stilbite were determined, using specially designed equipment. In the reversible adsorption range, heulandite shows no linearity breaks in the transforms and no structural variation. Stilbite, however, shows a linearity break in the transforms corresponding to a structural change.

Preparation of montmorillonite-nylon complexes and their thermal properties

Abstract: Montmorillonite-aminocaproic acid complexes (monomer complexes) were prepared by the intercalation of 6-aminocaproic acid to various homoionic (Na+, Ca2+, Mg2+, Co2+, and Cu2+) montmorillonites. Infrared spectra of the monomer complexes indicated that the interaction between the exchangeable cations and the 6-aminocaproic acid increased in the following order: Na-, Ca-, and Mg- < Co- < Cu-montmorillonite-aminocaproic acid complex. Montmorillonite-nylon complexes (polymer complexes) were prepared by thermal treatment of the monomer complexes, which was confirmed by X-ray powder diffraction and infrared spectroscopy the results of which indicated the condensation of 6-aminocaproic acid in the interlayer space. Thermal degradation of montmorillonite-nylon complexes was studied by thermogravimetry. It was found that the thermal stability of the polymer complexes increased in the following order: Cu- < Co- < Na- < Mg- < Ca-montmorillonite-nylon complex. It was suggested that the difference in thermal stability depended upon the length of the polymer chain which might be influenced by the interaction between the exchangeable cations and the 6-aminocaproic acid. The activation energy for the thermal degradation of each montmorillonite-nylon complex was obtained, and the value for Cu-montmorillonite-nylon complex was smaller than that for the other cation-exchanged montmorillonite-nylon complexes.

Ca-K Exchange Reaction and Interstratification in Montmorillonite

Abstract: Cation-exchange equilibrium for Ca-K-montmorillonite was studied at 35 ~ 50 ~ and 90~ and at three total normalities of the equilibrium solution (0.1, 0.05, and 0.01 N). Changes of the standard free energy for the exchange from K-montmorillonite to Ca-montmorillonite were determined to be - 53, - 270, and -393 cal/eq at 35 ~ 50 ~ and 90~ respectively. Changes of the standard enthalpy and entropy were 1.7 kcal/eq and 5.6 cal/eq/degree at 35~ respectively. The sign of the change of the standard free energy was found to be determined mainly by the entropy change, in particular, by the hydration entropy of the cations. The calculation of the excess functions indicates that the mixing model of Ca-K-montmorillonite ap- proximates that of a regular solution. Montmorillonite having potassium equivalent ion fraction of 0.1 to 0.7 consists of a random interstratification of Ca-montmorillonite (15.6 )~) and K-montmorillonite