Showing papers in "Clays and Clay Minerals in 1983"

Anion-exchange properties of hydrotalcite-like compounds

Abstract: Ion-exchange isotherms between hydrotalcite-like (HT) of the NO3-, CI-, and SO4- forms and F , 0% Br , I , OH-, SO42-, CO3 z-, and Naphthol Yellow S (NYS 2-) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH- > F > Cl > Br- > NO3- > I , those for divalent anions are in the sequence CO3 ~- > NYS z- > SO42- The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction

Effect of pH on the formation of goethite and hematite from ferrihydrite

Abstract: Storage of ferrihydrite in aqueous suspensions at 24°C and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. The crystallinity of both products, as indicated by X-ray powder diffraction line broadening and magnetic hyperfine field values and distribution widths, was poorer, the lower the proportion of the corresponding product in the mixture. The existence of two competitive formation processes is suggested: goethite is formed via solution, preferably from monovalent Fe(III) ions [Fe(OH)2+ and Fe(OH)4−], and hematite by internal rearrangement and dehydration within the ferrihydrite aggregates. This concept relates the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution, and implies that conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa.

Physicochemical properties of montmorillonite interlayered with cationic oxyaluminum pillars

Abstract: By ion exchanging expandable clay minerals with large, cationic oxyaluminum polymers, "pil- lars" were introduced that permanently prop open the clay layers. On the basis of thermal, infrared spec- troscopic, adsorption, and X-ray powder diffraction (XRD) analysis, the interlayering of commercial so- dium bentonite with aluminum chlorohydroxide, lAI1304(OH)24(HzO)12) +7, polymers appears to have produced an expanded clay with a surface area of 200-300 m2/g. The pillared product contained both Br6nsted and Lewis acid sites. XRD and differential scanning calorimetry measurements indicated that the micropore structure of this interlayered clay is stable to 540~ Between 540 ~ and 760~ the pillared day collapsed with a corresponding decrease in surface area (to 55 m2/g) and catalytic cracking activity for a Kuwait gas oil having a 260~176 boiling range.

Sorption of trace constituents from aqueous solutions onto secondary minerals; II, Radium

Abstract: Radium sorption efficiencies as a function of temperature, Ra concentration, and secondary mineral sorbate were determined in a 0.01 M NaCl solution. Radium sorption on a characterized clinoptilolite, montmorillonite, nontronite, opal, silica gel, illite, kaolinite, and glauconite under comparable experimental conditions allowed determination of Ra sorption efficiency curves for each, through use of Freundlich constants, over the same temperature and initial Ra solution concentration range. Similar sorption data for U on the same secondary minerals over the same temperatures allowed comparison of sorption efficiencies for Ra and U. Clinoptilolite, illite, and nontronite were the most efficient Ra sorbents, while opal and silica gel were the poorest Ra sorbents. Generally, Ra sorption on secondary minerals was much greater than U sorption under the same experimental conditions.

Infrared spectroscopic study of adsorbed water on reduced-charge Na/Li-montmorillonites

Abstract: Infrared (IR) spectra in the fundamental and near-IR regions were obtained for Na-saturated Wyoming montmoriUonite and reduced-charge Na/Li-saturated Wyoming montmorillonites hydrated un- der water vapor at 50% RH and dehydrated under vacuum. For the Na-montmorillonite, changes in the intensities of the structural OH-bending modes, particularly that of the MgA1OH group, were observed as the clay was dehydrated. This result was interpreted as evidence that exchangeable Na ions lose solvation water and settle into the ditrigonal cavities on the clay surface as it becomes desiccated. For the Na/Li- montmorillonites, the structural OH-bending modes also decreased in IR intensity because of Li § migration into the octahedral sheet. The fundamental IR spectra of D20 adsorbed by the montmorillonites showed characteristic absorptions at 2685, 2510, 2400, and 1205 cm 1 that decreased in intensity proportionally to the cation-exchange capacity. This result, along with corroborating data from X-ray powder diffractograms and from near-IR diffuse reflectance spectra of H20 adsorbed by the clays, suggest that the exchangeable cations on Na-montmoriUonite dissociated from the clay surface as it hydrated and played a significant role in organizing the structure of adsorbed water at low water contents.

Activity/composition relations among silicates and aqueous solutions; II, Chemical and thermodynamic consequences of ideal mixing of atoms on homological sites in montmorillonites, illites, and mixed-layer clays

Abstract: The activities of thermodynamic components of clay minerals corresponding in composition to pyrophyllite, muscovite, paragonite, and margarite were computed from chemical analyses reported in the literature assuming ideal mixing of atoms on homological sites in the minerals. These activities were then used to generate stability fields for smectites, illites, and mixed-layer clays on logarithmic activity diagrams representing equilibrium among minerals and aqueous solutions at 25°C and 1 bar. Comparative analysis indicates that the approach affords close approximation of both mineral and water compositions in geologic systems.

Further investigations of a conversion series of dioctahedral mica/smectites in the shinzan hydrothermal alteration area, northeast japan

Abstract: A complete conversion series for mica/smectites was found in a hydrothermal alteration envelope around Kuroko-type ore deposits at the Shinzan area, Akita Prefecture, Northeast Japan. The minerals are an alteration product of volcanic glass of Miocene age and are commonly associated with zeolites and silica minerals. Degrees of ordering of interstratification of the minerals change discontinuously from Reichweite g = 0 (100–55% expandable layers) to g = 1 (45–20% expandable layers), and from g = 1 to g = 2 (<20% expandable layers). This pattern of conversion differs from the behavior of mica/smectites during burial diagenesis which undergo a continuous change in ordering type, and from the behavior of rectorite which displays a constant expandability and ordering (45–55%) over a wide range of conditions. Differences between these minerals were also found in the relationships between expandability and total layer charge, and between expandability and number of non-exchangeable interlayer cations. In mica/smectites from the Shinzan area, chemical changes in the interlayers and tetrahedral and octahedral sites are consistent with a reaction in which K-enrichment and K-fixation in the interlayers are controlled by an increase in negative layer charge. This conversion occurred in response to a steep geothermal gradient and migrating hydrothermal solutions.

Clay minerals of Lake Abert, an alkaline, saline lake

Abstract: Mineralogical and chemical analyses of fine clay fractions from in and around Lake Abert, Lake County, Oregon, show that the pyroclastic rocks supplying detritus to the lake weather to a suite of layer silicate clay minerals varying from high-charge dioctahedral montmorillonite to montmorillonite/intergrade smectite-chlorite interstratifications. In the lake these clays extract K, Mg, and Si to form authigenic interstratified illite and a trioctahedral, Mg-rich mineral resembling stevensite in composition. Both the neoformed interstratifications contribute little unambiguously to X-ray powder diffraction patterns, which are dominated by the reflections of detrital clays. From limited data it appears that the illite occurs below 0.8 m depth in sediments of a possibly somewhat fresher (brackish) lake and the trioctahedral interstratification between 0.4 and 0.2 m depth in sediments of a lake of about the same size and salinity (about 30–90 g/kg) as that of the present lake. Минералогические и химические анализы мелких фракций глин, взятых изнутри и из окрестности озера Аберт в дистрикте Озеро в Орегоне, указывают, что пирокластические породы (которые доставляют детритус в озеро) выветриваются и образуют слоистые силикатовые глинистые минералы, отличающиеся по составу от заряженных двухоктаэдрических монтмориллонитов до переслаиваний монтмориллонит-смектит-хлорит. В озере эти глины извлекают из воды К, Mg, и Si для образования аутигенных переслаивающихся иллитов и триоктаэдрического, Mg-обогащенного минерала, напоминающего по составу стевенсит. Оба свежеобразованные переслаивания способствуют частично недвусмысленно рентгеновским порошковым диффрактограммам, в которых доминируют отражения детритовых глин. На основании ограниченных данных кажется, что иллит находится ниже глубины 0,8 м в осадках немного пресного озера (солоноватого), а триоктаэдрические переслаивания проявляются на глубине между 0,4 и 0,2 м в осадках озера примерно такого же самого размера и солености (около 30–90 г/кг), как существующего в настоящее время озера. [E.G.] Mineralogische und chemische Analysen von feinen Tonfraktionen aus dem Innern und vom Rand des Lake Abert, Lake County, Oregon, zeigen, das pyroklastische Gesteine Gesteinsschutt in den See liefern, der zu einer Abfolge von Tonmineralen verwittert, die von stark beladenem dioktaedrischem Montmorillonit bis Montmorillonit/Smektit-bzw. Montmorillonit/Chlorit-Wechsellagerungen variieren. Im See extrahieren diese Tone K, Mg, und Si, um autigene Illit-Wechsellagerungen und ein trioktaedrisches Mg-reiches Mineral, das in der Zusammensetzung mit Stevensit vergleichbar ist, zu bilden. Beide neugebildeten Wechsellagerungen tragen wenig eindeutige Reflexe zur Rontgenpulveraufnahme bei, die vor allem die Reflexe der detritischen Tone zeigt. Aus den begrenzten Daten geht hervor, das der Illit unter 0,8 m Tiefe in den Sedimenten eines moglicherweise etwas frischeren (brackischen) Sees auftreten und die triok-taedrischen Wechsellagerungen zwischen 0,4 und 0,2 m Tiefe in Sedimenten eines Sees, der etwa die gleiche Grose und die gleiche Salinitat aufweist (etwa 30–90 g/kg) wie der gegenwartige See. [U.W.] Des analyses mineralogiques et chimiques de fractions d’argile fines provenant de l’interieur et d’autour du Lac Abert, Lake County, Oregon, montrent que les roches pyroclastiques fournissant du detritus au lac s’alterent en une suite de mineraux argileux silicates variant de montmorillonite dioctaedrale a haute charge a des interstratifications montmorillonite/smectite-chlorite intergrade. Dans le lac, ces argiles extraient K, Mg, et Si pour former de l’illite authigenique interstratifiee et un mineral riche en Mg ressemblant a la stevensite. Ces deux interstratifications nouvellement formees contribuent peu sans ambiguite aux cliches de diffraction poudree des rayons-X, qui sont domines par les reflections des argiles detritiques. A partir de donnees limitees il semble que l’illite se trouve sous une profondeur de 0,8 m dans les sediments d’un lac possiblement a eau plus fraiche (saumure), et que l’interstratification trioctaedrale se trouve entre 0,4 et 0,2 m de profondeur dans les sediments d’un lac d’a peu pres la meme taille et de meme salinite (~30–90 g/kg) que celles du lac present. [D.J.]

Sorption of uranium and radium by biotite, muscovite, and phlogopite

Abstract: The sorption of U and Ra on finely ground biotite, muscovite, and phlogopite was adequately described by the Freundlicb adsorption equation, (x/m) = KC n, at low U and Ra concentrations despite Ra precipitation at the higher temperature. Radium and U sorption-efficiency curves derived from the Freundlich constants generally showed decreased distribution coefficients in response to increasing lem- perature and increasing Ra or U concentrations. Temperatures investigated were 5~ 25~ and 65~ Solution compositions used were 0.1 M NaC1 and 0.01 M NaHCO3 for U, and 0.01 M NaC1 for Ra. Uranium initial solution concenlrations ranged from 1.00  10 4 M to 4.00  10 7 M; the Ra initial solution concentration range was 6.80  10 -7 M to 8.60  10 9 M. In 0.01 M NaHCO3 solutions, anionic uranyl carbonate complexes were prevalent, and because they are weakly sorbed relative to free uranyl ion and uranyl hydroxy complexes, the result was a relatively low U sorption efficiency on biotite and phlogopite and excellent sorption efficiency on muscovite. Uranyl carbonate complexes decreased in solubility with increasing temperature, so that U sorption efficiency on biotite increased with increasing temperature. Sorption of uranyl ion and uranyl hydroxy cations on biotite decreased with incresaing temperature.

Potassium Fixation by Clay Minerals during Hydrothermal Treatment

Abstract: The amount of K fixed in K- and Ca-saturated montmorillonite, vermiculite (trioctahedral), rectorite-type and IMII-ordered mica/montmorillonites was measured as a function of time (1–64 days), temperature (25o-300°C), pH (6.0, 9.7, and 10.7), and K-concentration (0.02 and 1.0 M) in solution. The amount of K fixed by the clays generally increased with increasing temperature, pH, and K-concentration and reached saturation in response to each experimental condition in 5 or 6 days. The K-montmorillonite and K-vermiculite fixed considerable amounts of K even at 25°C. Fixed K in montmorillonite increased with an increase of the layer charge which is also influenced significantly by the interlayer cation. In detail, the behavior in K-fixation was specific to each clay. The type of structural transformation with K-fixation was different for each clay. In montmorillonite, especially, the type of transformation was related to the cationic composition of the system; in K homoionic system, montmorillonite transformed rapidly into illite/montmorillonite with about 40% expandable layers at 300°C and in a mixed cation system with Ca and K, it reacted gradually to random illite/montmorillonites with increasing temperature. These data indicate that the cation-exchange process of a natural pore solution plays an important role in the gradual transformation of detrital montmorillonite to illite.

Origin of berthierine in ironstones

Abstract: To test the hypothesis that berthierine in oolitic ironstones formed by diagenetic transformation of detrital kaolinite, laboratory experiments simulating the early diagenetic conditions were conducted. Representative sets of the initial sediment were prepared in distilled water and artificial seawater suspen- sions by mixing 4-13 g/liter kaolinite with Fe(OH)a precipitated from 0.1-0.3 M FeClz solutions. ~NazS204 was added to the suspensions as a reducing agent, and inert Nz atmospheres were used to maintain the required Eh between + 100 and -400 mV. The pH of the suspensions was controlled between 8 and 5 with dilute HC1. Within 300 days, the iron content of the bulk kaolinite in the seawater suspensions progressively increased from 0.18 to 2.44% at pH = 7 and Eh between -250 and -350 mV. Energy dispersive X-ray analyses of individual clay platelets in the final products showed progressive, temporal increase in Fe, and concomitant decrease in AI and Si. X-ray powder diffractometry revealed small d(001)-d(002) shifts, marked intensity reversals of (001) and (002) reflections, and the development of additional characteristic berthier- ine reflections with time. These data suggest progressive transformation of kaolinite to berthierine. Mi- croprobe analyses of natural berthierine in oolitic ironstones also showed parallel patterns, which sub- stantiate such progressive transformation from the margin toward the core of the ooids. The transformation did not take place in distilled water. The addition of Mg 2§ to the distilled water suspensions, however, promoted the transformation.

Atom positions in highly ordered kaolinite

Abstract: The crystal structure of kaolinite(Pl, a = 5.153(1), b = 8.941 (1), c = 7.403 (1)A, α = 91.692(3)°, β = 104.860(3)°, γ = 89.822(3)°, specimens from Keokuk geodes) has been refined in detail and that of dickite (Cc, a = 5.1460(3), b = 8.9376(5), c = 14.4244(6) A, β = 96.761(5)°) has been re-refined, both from powder diffraction data with the Rietveld method. Except for the hydrogen atoms, the layer structures in both clays are very similar and are much as inferred or determined previously by others. The rotation in the tetrahedral sheet is 7(1)°. The two inner hydroxyl O-H bonds in kaolinite are differently oriented; one points into an octahedral vacancy and the other somewhat away from the octahedral sheet and toward the unoccupied center of an oxygen triangle formed by the two apical oxygens and shared basal oxygen of two adjacent SiO4 tetrahedra. All six of the inner surface hydrogen atoms appear to be nearly equally involved in the hydrogen bonding between kaolinite layers in kaolinite.

Adsorption of quinoline from aqueous solutions by some clays and oxides

Abstract: The adsorption isotherms of quinoline from aqueous solutions by some clays and oxides varied from the S type for silica to a form somewhat similar to the Langmuir type for montmorillonite and silica- alumina. The adsorption reaction reached equilibrium in about 2 hr and was irreversible. X-ray powder diffraction studies showed that a single layer of molecules is adsorbed on montmorillonite and that the molecules lie either flat or in an upright position depending on surface coverage. The adsorption showed high sensitivity towards pH, attaining a maximum at pH 6. The decrease below pH 6 was due to competition with protons as well as to problems inherent in surface packing of positively charged quinoline molecules. The decrease above pH 6 is probably due to more exchangeable metallic cations on the surface leading to a favored sorption of water over organic molecules.

Hydrogen Atom Positions in Kaolinite by Neutron Profile Refinement

Abstract: A structure refinement of kaolinite made using the Rietveld neutron profile refinement tech- nique has given non-hydrogen atom positions which were not significantly different from those given by B. B. Zvyagin in i960. All of the hydrogen atoms have been located; the three inner-surface hydrogen atoms are involved in interlayer hydrogen bonds with lengths of 2.95(4), 2.95(4), and 3.06(4) )k with O-H... O angles of 168(4) ~ 144(4) ~ and 146(4) ~ respectively. The inner hydrogen atom is located in a position consistent with that found earlier in dickite and muscovite which are the only dioctahedral layer silicates studied by neutron diffraction to date. The O-H vector makes an angle of 34 ~ with the (001) plane, away from the octahedral sheet, and the projection of the vector on to (001) is at ~30 ~ to the b axis.

Fourier transform infrared studies of aluminous goethites and hematites

Abstract: Synthetic aluminous hematites and goethites have been examined by Fourier-transform in- frared spectroscopy. For aluminous hematites prepared at 950~ a linear relationship exists between AI content and the location of the band near 470 cm ~, up to 10 mole % AI substitution which is shown to be the solubility limit. The spectra of aluminous goethites prepared in two different ways are qualitatively similar to each other, but differ as to the relationship between the position of the band near 900 cm -1 and the A1 content. The spectra of the two series of hematites produced by calcining the goethites at 590~ also show a strong dependence of band position and intensity on the goethite preparative method.

Intergradient vermiculite-kaolin mineral in a Korean Ultisol

Abstract: A 14-A mineral coexisting with kaolin minerals, mica, and gibbsite in a Korean Ultisol and showing X-ray powder diffraction features of “chloritized” vermiculite was studied by a combination of methods The 14-A mineral collapsed on saturation with K+ after extraction with hot 1/3 M sodium citrate, but the Si/Al ratio of the extracted material was close to 10 and kaolin minerals dissolved, as indicated by difference infrared spectroscopy The 14-A mineral was also collapsed by heating at or above 350°C The difference infrared spectra and the X-ray powder diffraction patterns indicated that two forms of kaolin mineral are present that differ in thermal stability; one decomposed by heating at or below 375°C and the other by heating above 375°C The former kaolin mineral is probably associated with vermiculite and the latter is present as a discrete form The 14-A mineral was inferred to be an intergradient vermiculite-kaolin mineral, in which most vermiculite layers each partially transform into double kaolin layers, and to represent an intermediate phase during the transformation of 2:1 to 1:1 layer silicates in acid soils

Rubification of Terrae Rossae in Slovakia: A Mössbauer Effect Study

Abstract: Mineralogical and mFe Mrssbauer spectroscopic analyses were made on seven terrae rossae and two terraefuscae samples of Pliocene to Early Pleistocene age from Slovakia and limestone residues from their parent materials. In most of the samples, no mineral weathering or clay mineral formation could be detected by optical or X-ray powder diffraction investigation, compared with their parent limestone residues; only one terra rossa showed a strong weathering of primary feldspar and phyllosilicates and a high rate of clay formation, especially kaolinite. Mrssbauer measurements between 5 ~ and 300~ showed that hematite and goethite are the dominant color pigments in the rubified terrae rossae and their corre- sponding limestone residues. The mean particle size of hematite and goethite was estimated from Mrss- bauer effects and X-ray powder diffraction data to be 95 and 250 A, respectively. Reduced values of the hyperfine fields at 5~ of the soil iron oxides, as compared with those of the pure oxides, indicate a partial substitution of Fe(III) by A1. The hematite content correlates with the Munsell color notation of 5 of the 7 terrae rossae samples and their corresponding limestone residues. All terrae rossae samples showed higher hematite contents than their corresponding limestone residues, indicating that the rubification of such ma- terials is independent of the degree of weathering.

Infrared Studies of Ni-bearing Clay-minerals of the Kerolite-pimelite Series

Abstract: Two kerolite and one garnierite samples were subjected to progressive heat treatments prior to their examination by infrared spectroscopy (IR) in the 1200-600-cm−1 and 3800-3000-cm−1 regions. The heat treatment of the garnierite (a mixture of nepouite and pimelite) selectively dehydroxylated the nepouite thus allowing an examination to be made of the OH-vibration bands due to the pimelite. Both the relative intensities of the 710-670-cm−1 doublet and of the different OH-stretching bands indicated the Ni content of this pimelite to be about 70%. The heat treatments did not modify the 1200-600-cm−1 region of the spectra of kerolites but caused a noticeable sharpening in the OH-stretching region. The relative intensities of the structural OH-stretching bands of dehydrated kerolites showed that they differ from Ni-talcs of similar composition in the distribution of Ni and Mg in the octahedral sites. These cations are randomly distributed in Ni-talc but are mainly segregated into Mg and Ni domains in kerolite. Changes in sharpness, intensity, and position of the structural OH-stretching bands of the kerolites as temperature increases and dehydration progresses are similar to those undergone by Mg- or Li-saturated trioctahedral smectites. Also thermal analysis curves of these minerals show similarities with those of Mg- and Ni-saturated smectites, and suggest that in kerolites too, the hydration water is associated with interlayer (though non-exchangeable) Ni and/or Mg cations.

Mössbauer Effect Studies of Iron in Kaolin. I. Structural Iron

Abstract: 57Fe Mossbauer spectra of a cleaned Weipa, Australia, kaolin showed that a considerable fraction of the structural iron exhibits paramagnetic relaxation between 4°K and 300°K, the first time that this has been observed for ferric ions in a mineral. The sample also contained a very fine particle ferric oxide/oxyhydroxide phase, probably of secondary origin.

Reactions of alcohols with alkenes over an aluminum-exchanged montmorillonite

Abstract: The reaction of 2-methyl pent-2-ene with primary alcohols (CI-Cls) at 95~ over an Al-mont- morillonite gave yields of 20-90% of ethers of the type R-O-C(CH3)2CaHT. Lower yields were produced if secondary alcohols were employed, and tertiary alcohols gave only a trace of this ether. When a variety of alkenes was reacted with bntan-l-ol at 95~ over a similar catalyst, no reaction occurred unless the alkene was capable of forming a tertiary carbonium ion immediately upon protonation. In this case the product was the tertiary ether t-R-O-nC4H9. However, at a reaction temperature of 150~ a variety of products were formed including (1) ether by the attack of butanol on the carbonium ions produced either directly from protonation of the alkenes or by hydride shift from such an ion, (2) alkenes by the attack of n-C4Ha § ions (derived from protonation and dehydration of butanol) on the alkene, (3) di-(but-1-yl) ether by dehydration of the butanol, and (4) small amounts of alcohol by hydration of the alkene. The differences in reactivity below and above 100~ are related directly to the amount of water present in the interlayer space of the clay and the degree of acidity found there. Although the clay behaves as an acid catalyst, the reactions are far cleaner (more selective) than comparable reactions catalyzed by sulfuric acid.

Charge heterogeneity in smectites

Abstract: The heterogeneity of sites for Ca→K exchange was examined by microcalorimetry in the <0.2-μm fractions of some selected smectites. Six groups of sites, ranging in exothermic exchange enthalpy (-d(ΔHx)/dx) from 5.7 to 10.9 kJ/eq were identified. In Wyoming bentonites, only three groups with enthalpies of 5.7 to 7.5 kJ/eq were distinguished, although in the 0.2-1.0-μm fraction, a 10.7-kJ/eq group was also observed. Redhill and Camp Berteau smectites contained, in addition, groups with enthalpies of 8.7-10.9 kJ/eq, but a New Mexico sample only had groups with the higher values. Thus, the exchange enthalpies of four main groups of sites (reclassified from those observed) appear to be inversely related to the extents of interlayer expansion in the samples by the adsorption of polar molecules. Consequently, a ’true mont-morillonite,’ such as a <0.2-μm Wyoming bentonite, contains only fully expanding layers with -d(ΔHx)/ dx values between 5.7 and 7.5 kJ/eq. As such, it is less heterogeneous and should have a much greater swelling capability than Camp Berteau montmorillonite which has, in addition, groups with exchange enthalpies of 8.7 and 10.3 kJ/eq.

Hydrothermal Reactivity of Saponite

Abstract: Saponite crystallizes from amorphous gel having an ideal saponite composition within 7 days at all experimental temperatures between 300° and 550°C at 1 kbar pressure. Reactions subsequent to this initial crystallization vary in type and degree, depending on the temperature of reaction and the type of interlayer cation. Above 450°C, the intitially crystallized K-saponite dissolves, and talc and phlogopite nucleate and grow as discrete phases. At 450°C the initial K-saponite reacts to form talc and phlogopite layers, but the reaction proceeds via intracrystalline layer transformations rather than via dissolution and precipitation, producing a mixture of fully ordered, interstratified talc/saponite and fully ordered saponite/ phlogopite. The K-saponite shows subtle signs of reaction at 400°C after 200 days: this temperature is at least 150°C lower than experimental reaction temperatures previously reported for saponites. No reactions beyond the initial crystallization of saponite were observed below 400°C. K-saponite reacts more rapidly than either Na-saponite or Ca-saponite above 400°C, and the Na-saponite and Ca-saponite produce no mica layers during their transformation to mixed-layer clays. Interstratified talc/saponite formed in the Na-saponite system, and the Ca-saponite system produced both talc/saponite and chlorite/saponite.ZusammenfassungSaponit kristallisiert aus einem amorphen Gel, das eine ideale Saponitzusammensetzung hat, innerhalb von 7 Tagen bei allen experimentellen Temperaturen zwischen 300° und 550°C und einem Druck von 1 kbar. Die Reaktionen nach dieser anfänglichen Kristallisation variieren in Art und Ausmaß je nach Reaktionstemperatur und Art der Zwischenschichtkationen. Über 450°C löst sich der anfänglich kristallisierte K-Saponit wieder auf, und Talk und Phlogopit wachsen als diskrete Phasen. Bei 450°C reagiert der ursprüngliche K-Saponit und bildet Talk- und Phlogopit-Lagen. Diese Reaktion verläuft jedoch über intrakristalline Lagenumwandlung und weniger über Auflösung und Ausfällung. Dabei bildet sich ein Gemenge aus einer vollständig geordneten Talk/Saponit-Wechsellagerung und einer vollständig geordneten Saponit/Phlogopit-Wechsellagerung. Der K-Saponit zeigt bei 400°C nach 200 Tagen gewisse Anzeigen einer Reaktion. Diese Temperatur ist mindestens um 150°C niedriger als experimentelle Reaktionstemperaturen, die bisher für Saponit berichtet wurden. Unter 400°C wurde nach der anfänglichen Saponit-Kristallisation keine weitere Reaktion beobachtet. K-Saponit reagiert über 400°C schneller als Na-Saponit oder Ca-Sa-ponit. Außerdem bilden sich aus Na-Saponit und Ca-Saponit keine Glimmerlagen während ihrer Umwandlung zu Wechsellagerungen. Talk/Saponit-Wechsellagerungen, die im Na-Saponit-System und im Ca-Sa-ponit-System gebildet wurden, führten zur Bildung einer Talk/Saponit- und einer Chlorit/Saponit-Wechsellagerung. [U.W.]RésuméLa saponite se cristallise à partir d’un gel amorphe ayant une composition saponite idéale endéans 7 jours à toutes les températures expérimentales entre 300° et 550°C sous une pression d’ 1 kbar. Les réactions subséquentes à cette cristallisation initiale varient de type et de degré, dépendant de la température de la réaction et du genre de cation intercouche. Au dessus de 450°C, la saponite-K initialement cristallisée se dissout, et du talc et de la phlogopite deviennent nucléés et croissent en phases discrètes. A 450°C la saponite-K initiale réagit pour former des couches de talc et de phlogopite, mais la réaction se produit via des transformations de couche intracristallines plutôt que via une dissolution et une précipitation, produisant un mélange de talc/saponite interstratifié complètement ordonné et de saponite/phlogopite complètement ordonné. La saponite-K montre des signes subtiles de réaction à 400°C après 200 jours: cette température est au moins 150°C plus basse que les températures de réaction expérimentales rapportées auparavant pour des saponites. On n’a observé aucune réaction au-delá de la cristallisation initiale de saponite sous 400°C. La saponite-K reagit plus rapidement que soit la saponite-Na ou la saponite-Ca au dessus de 400°C et la saponite-Na et la saponite-Ca ne produisent pas de couche de mica pendant leur transformation en argiles à couches mélangées. Le talc/saponite interstratifié a été formé dans le système saponite-Na, et le système saponite-Ca a produit à la fois du talc/saponite et de la chlorite/saponite. [D.J.]АбстракцияСапонит кристаллизировался из аморфного геля, имеющего идеальный сапонитовый состав, в течение 7 дней при всех экспериментальных температурах в диапазоне от 300° до 550°С и при давлении 1 кбар. Реакции, следующие за этой первоначальной кристаллизацией, различаются типом и степенью в зависимости от температуры реакции и типа межслойного катиона. Выше 450°С, первоначально выкристаллизированный К-сапонит растворяется, а тальк и флогопит образуют центры кристаллизации и растут как дискретные фазы. При 450°С первоначально образованный К-сапонит реагирует, образуя слои талька и флогопита. Эта реакция происходит скорее путем внутрикристаллических трансформации слоев, чем путем растворения и осаждения. Продуктом реакции является смесь полностью упорядоченных талька/сапонита и сапонита/ флогопита. К-сапонит проявляет слабые признаки реакции при 400°С после 200 дней. Температура 400°С является по крайней мере на 150°С ниже, чем экспериментальные температуры реакции, ранее опубликованные для сапонитов. Ниже 400°С не наблюдались никакие реакции кроме начальной кристаллизации сапонита. Выше 400°С К-сапонит реагирует более быстро, чем Na-сапонит или Са-сапонит. Nа-сапонит и Са-сапонит не формируют слои слюды во время их трансформацйй в смешано-слойные глины. Переслаивающийся тальк/сапонит, формировался в системе Na-сапонит, а оба, тальк/сапонит и хлорит/сапонит формировались в системе Са-сапонита. [Е.С.]

Spherical kaolinite; synthesis and mineralogical properties

Abstract: Spherical kaolinite has been synthesized for the first time from noncrystalline aluminosilicate material in hydrothermal experiments conducted between 150° and 250°C and under autogenous vapor pressure. Spherules, whose mean diameters depended on growth conditions (0.1–0.6 μm), were formed surrounding the noncrystalline aluminosilicate in all products of 150° and 200°C runs and coexisted with platy or lath-shaped kaolinite in the products of 250°C runs. The estimated percentages of spherules in the products increased from about 1% in the 150°C-15 days product to about 74% in 200°C-8 days product, and decreased from about 21% in 250°C-2 days product to 0% in 250°C-8 days product. Lattice images by high-resolution electron microscope indicated that the spherules consisted of nearly concentric stackings of layers with a unit spacing of 7A, which were sectored by radiating boundaries. The mean chemical composition of the spherules (Al2O3/SiO2 = 0.58) analyzed by the analytical electron microscope is similar to that of kaolinite (Al2O3/SiO2 = 0.5). Even in the case of the product abundant in spherule (200°C-8 days), X-ray powder diffraction patterns of the wetted products, e.g., of the 200°C-8 day run, showed the 7.14-A (001) reflection of kaolinite. The 020 reflection was broad, indicating the existence of abundant (001) layer displacements. The b axis (8.94 A) were within the kaolinite range (8.93–8.94 A). No infrared absorption peaks were observed at 3550 cm−1 which would correspond to halloysite. The differential thermal analysis slope ratios of the endothermic peak at about 550°C (1.4–2.3) were in the kaolinite range (0.78–2.39).

Role of ferric iron in the oxidation of hydrocortisone by sepiolite and palygorskite

Abstract: The role of adsorbed and structural Fe3+ in palygorskite and sepiolite with respect to the oxidation of hydrocortisone in aqueous suspension has been evaluated using electron spin resonance and UV-visible spectroscopy. Natural surface-adsorbed Fe3+ showed an important activity in the oxidation process, although smaller than octahedral Fe3+. The kinetics of oxidative degradation of hydrocortisone by palygorskite appear to be composed of two apparent first order reactions which may be associated with two kinds of sites for Fe in palygorskite. The lower oxidizing power of sepiolite for hydrocortisone degradation is due to its very low Fe3+ content.

Crystal Structure of Cronstedtite-2H2

Abstract: The crystal structure of a magnesian cronstedtite-2H2 from P~l'bram, Czechoslovakia, was re- fined in space group C 1 to a residual of 5.4% with 1832 independent reflections. Tetrahedral ordering be- tween Fe a+ and Si is judged to be complete on the basis of electron density maps, the first confirmation of such ordering in a layer silicate. Octahedral cations are disordered on the M sites. Mean T-O bond lengths do not confirm the tetrahedral ordering, perhaps due to tetrahedral distortion in order to relieve the extreme corrugation of the sheet that would arise from ordering of such different size cations. In the initial stages of refinement the structure of the crystal under study could not be described ade- quately on the basis of a single 2H2 polytype. The structure contains two kinds of 2Hz domains that appear shifted by b/3 relative to one another due to a mistake in the interlayer stacking sequence. This mistake of zero shift (the normal 2H~ polytype consists of alternating -b/3 and +b/3 shifts) affects only the tetrahedral sheets. It creates adjacent enantiomorphic domains of 2H z packets such that domains with small Si tetra- hedra sit above larger FeZ+-rich tetrahedra and vice versa. This mechanism to relieve strain may indeed be the cause of the stacking mistakes. A third kind of domain contains regions in which the sense of tet- rahedral rotation is reversed, giving rise to split basal oxygens on electron density maps. This multiple domain model best explains extra atomic positions observed on Fourier maps, lack of streaking of k ~ 3n reflections, and possible nonintegral "satellitic" reflections observed on Weissenberg films.