Showing papers in "Clays and Clay Minerals in 1972"

Selective sorption and fixation of cations by clay minerals : A review

Abstract: Investigations concerning selective sorption and fixation of K and similar cations by clay minerals and soil clays and the mechanisms of these reactions are reviewed. In particular, recent observations on selective sorption of these ions in dilute solutions by weathered micas and vermiculite in relation to the interlayer structures are discussed in detail. Also, implications of the resistance to weathering of small mica particles to cation selectivity by soils are described. Despite the increased understanding of sorption and fixation reactions, the following aspects remain unclear. First, the mechanism of the collapse of alternate layers in vermiculite on K or Cs sorption has not been unequivocally established. Second, factors that impart stability to the central core of mica particles so that K extraction becomes progressively difficult are not known. Third, inability of Ca or Mg ions to expand interlayers of Cs-saturated vermiculite in contrast to K-saturated vermiculite is not completely understood.

A ferroan nontronite from the red sea geothermal system

Abstract: A smectite rich in ferrous iron and low in aluminum occurs abundantly in the Red Sea Geothermal Deposits, and appear to be forming at present. Chemical analyses and M/Assbauer spectra indicate the mineral is intermediate in composition between nontronite and the as yet undescribed trioctahedral ferrous iron end member.

The transformation of lepidocrocite to goethite

Abstract: The conversion of lepidocrocite (-γFeOOH) to its more stable polymorph, goethite (αFeOOH) was followed by observing changes in crystal morphology, oxalate solubility, surface area and X-ray diffraction. In conjunction, kinetics were measured as functions of surface area, temperature, alkalinity and seeding with goethite crystals.

The Influence of Silicate on the Transformation of Lepidocrocite to Goethite

Abstract: The mechanism of the transformation of lepidocrocite (γFeOOH) to goethite (αFeOOH) has previously been established and the effect of silicate on the transformation was investigated Rather than completely inhibiting the reaction, as had been suggested, the presence of Si was found to merely retard the nucleation stage of the transformation There was found to be no decrease in the dissolution rate of the lepidocrocite due to surface adsorption of Si Si has no effect if introduced after the nucleation stage, and under conditions of pH and temperature where the dissolution rate of the lepidocrocite largely determines the rate of transformation, the presence of Si has a reduced effect The results show that Si is adsorbed and incorporated into the goethite structure, and due to its retarding effect on the nucleation, larger crystals of goethite are formed, many of which are twinned It is inferred from the results that the apparent stability of lepidocrocite occurring in soils in association with goethite cannot be attributed solely to the presence of Si in the soil system

Geochemical mechanics for the dissolution, transport, and deposition of aluminum in the zone of weathering

Abstract: Organic acids in the 0-01M concentration range representing amino-, aliphatic, and aro- matic types present in humus dissolve 70-85 ppm A1 from Arkansas bauxite at room temperature, whereas 0-03 ppm is dissolved in water. The species of A1 in aqueous solution, calculated from stability data, range from A13+ at pH 3 and lower, through AI2(OH)24+ at a maximum concentration at pH 4.5, AI(OH) 2+ at a maximum at pH 4.7, AI(OH)2 + at a maximum at pH 6.0, to AI(OH)4- at pH 8.5 and higher. In salicylic acid an Al-Sal + complex occurs between pH 1"5 and 8.5, and is at a maximum at pH 4.2. Solubility of A1 obviously is pH dependent; also because of the vulnerability of organic acids to oxidation, the solubility and transport of A1 is indirectly Eh dependent. Anions that combine with Al include OH- to form bauxite, PO43- to form lateritic phosphate such as the Bone Valley Formation, Fla., and SiO4 4- to form allophane or kaolin as noted in the kaolin synthesis by Linares and Huartes. Spongelike, pisolitic or oolitic structures, and mineral veins in bauxites, lateritic phos- phates, and some flint clays attest to mobilization of Al in solution. Lignites and humus zones associa- ted with laterites are a logical geologic source of these complexing organic solvents. Although Al is inherently mobile, such commonly available precipitating anions render A1 relatively immobile.

RELATION BETWEEN SWELLING, WATER PROPERTIES AND b-DIMENSION IN MONTMORILLONITE- WATER SYSTEMS*

Abstract: The b-dimensions of the unit cells of six different Na-saturated montmorillonites were determined by X-ray diffraction at water contents ranging from 0 to 20 g per g of montmorillonite. In every case, the b-dimension increased progressively with water content from its initial value, which was characteristic of each dry montmorillonite, to a final value of ~9•0A, which was common to all montmorillonites. The latter value was reached when the water contents of the respective montmorillonites were equal to those at maximal swelling. When these water contents were plotted against the corresponding changes in b-dimension, a straight line that passed through the origin was obtained. Different structure-sensitive properties of the water in montmorillonite-water systems (i.e. the partial specific volume, the amount remaining unfrozen at −5°C and the activation energy required for ions to move through it) were available, as functions of the species of exchangeable cation, from previous studies. Relevant b-dimensions were determined in the present study. It was found that all of these water properties were correlated with the b-dimension of the associated montmorillonite. Our results indicate that epitaxy exists between the crystal lattices of montmorillonite and adsorbed water and that these lattices undergo mutual adjustment with each increment of water. The resulting loss of free energy causes water adsorption, i.e. swelling, to occur spontaneously. Swelling stops when no further adjustment takes place. This does not happen until the adsorbed water is several hundred angstroms thick and has achieved a preferred configuration.

The Oxidation of Octahedral Iron in Biotite

Abstract: Oxidation of octahedral ferrous iron in biotite by saturated bromine water results in a loss of both octahedral and interlayer cations. The hydroxyl adjacent to vacant octahedral cation sites adopt an inclined orientation resulting in a more stable environment for interlayer cations. The only structural change accompanying these processes is a decrease in b-axis dimension which is linearly related to octahedral ferric iron content. These findings are in agreement with observations made on naturally weathered biotites.

Thermodynamics of the Exchange of n-Alkylammonium Ions on Na-Montmorillonite

Abstract: A thermodynamic study has been made of the ion exchange equilibria of the n-alkylam- monium ions in sodium montmofillonite. Exchange isotherms of ammonium, methylammonium, ethylammonium, propylammonium and butylammonium with sodium montmorillonite were deter- mined at 4 ~ 25 ~ and 55~ From these data the changes in free energy, enthalpy and entropy for the exchange reactions were calculated. In the temperature region used in this work, no enthalpy change was observed. Thus the exchange was only controlled by entropy effects. The thermodynamic excess functions were calculated from the surface activity coefficients. The affinity of the organic ions for the clay increases with chain length. It is shown that this increase can not be ascribed to van der Waals forces, but must be due to the combined effect of variations in electrostatic interactions with the clay lattice and of the hydration state.

The Relationship Between the Hydrated and Dehydrated States of an Halloysite

Abstract: A study of the mineralogical changes taking place during the loss of interlayer water in an halloysite has been carried out in order to clarify the relationship between the most hydrated and least hydrated states of the mineral. A number of samples of halloysite which together exhibit a variety of average interlayer water capacities were obtained by the conditioning of a largely hydrated sample with different atmospheres of known relative humidities. Profiles were obtained of X-ray peaks which characterize the interlayer water capacities of halloysite samples. An attempt has been made to analyse these profiles into a sum of peaks attributable to the fully hydrated and dehydrated states of the mineral. Such an analysis does not satisfactorily explain the profile shapes. A mechanism of interstratification of hydrated and dehydrated kaolin layers in which there is a tendency towards the segregation of these layer types gives a more satisfactory explanation of these profile shapes. It is concluded that dehydration takes place through an interstratification in which there is a partial segregation of the two basic layer types. This conclusion implies that halloysites with all average interlayer water contents between 0 and 2 molecules per unit cell may exist and that fully hydrated halloysite and dehydrated halloysite are the end members of a continuous series of hydration states.

The Stability of Gibbsite and Boehmite at the Surface of the Earth

Abstract: Two mutually exclusive views exist concerning the relative stabilities of gibbsite and boehmite in soils. These are examined in terms of experimental and thermodynamic evidence and it is shown that all three possible divariant assemblages of two phases that can exist between gibbsite, beohmite and H2O, may do so at 25°C and 1 atmosphere total pressure depending on the status of H2O. It is further shown that the conditions of H2O chemical potential needed to stabilize boehmite + H2O relative to gibbsite + H2O or gibbsite + boehmite, are unlikely to occur in natural waters in the zone of weathering.

The chlorite series of flagstaff hill area, california: a preliminary investigation

Abstract: The results of X-ray diffraction, DTA, i.r. spectroscopy, and chemical tests are presented for some chlorites typical of the Flagstaff Hill area. The area is notable for the large variety of chlorite types occurring in considerable quantities. Chlorite, in this area, is found as veins, as pseudomorphs, and as individual crystals. Textures vary from massive, fine-grained aggregates to books which are more than 20 mm in width. Crystals more than 5 mm in size occur in parallel groupings at rock interfaces. Judging from 45 chlorite samples studied, sheridanite is most abundant; clinochlore and ripidolite are common. Penninite and its Cr-chlorite equivalent are less abundant. The parent rock is an irregularly shaped ultramafic body surrounded by low-grade schists and located very close to a granodiorite stock. The original ultramafic rocks have been highly altered by metamorphism and metosomatism into assemblages comprised mainly of serpentine, talc, hornblende, and chlorite with relics of olivine, pyroxene, and other less abundant original minerals. Much of the exposed rock is essentially monomineralic, mostly consisting of various polytypes of serpentine. Preliminary investigation indicates that the area merits much more study because of the opportunity for readily observing the various chlorite types and determining their genesis, alteration sequences and weathering characteristics. The area, being easily accessible, could also serve as an adequate source for samples to be used as reference standards.

Imogolite and allophane formed in saprolite of basalt on Maui, Hawaii

Abstract: Inorganic gel and allophane collected from basaltic saprolite on Maui, Hawaii, and studied by Patterson in 1964 were reexamined. The main constituent of the gel is imogolite, and gibbsite and allophane are the minor constituents. Electron and X-ray diffraction patterns, DTA curve, and an infrared spectrum of the gel are characteristic of imogolite. The allophane is virtually noncrystalline to X-rays but contains a small amount of imogolite in relatively short threads. High-resolution electron micrographs indicate differences in structural organization between allophane and imogolite and suggest crystallization of imogolite from allophane. The occurrence of imogolite as a weathering product has been reported in many localities from pyroclastic materials but not from massive rocks. Probably the exceptionally high rainfall, excellent subsurface permeability of the weathered material, and the low pH and high organic content of the leaching solution provide favorable conditions for formation of imogolite from basalt on Maui.

The Occurrence of Sepiolite and Attapulgite on the Southern High Plains

Abstract: Sepiolite and attapulgite have been found to be common, sometimes the major, clay minerals in calcareous lacustrine deposits on the southern High Plains in West Texas and eastern New Mexico. Deflation debris derived from the basins and calcareous soils developed in the debris and in the lacustrine deposits also often contain either or both minerals. Dolomite is the carbonate commonly associated with sepiolite and calcite has a similar relationship to attapulgite in the lacus- trine deposits. Pedogenic formation of sepiolite and attapulgite appears unlikely in the area studied since an association with lacustrine materials was made in a very high percentage of the occurrences. Sepiolite was found to be highly concentrated in the < 0.2ft fraction. A similar, but less pro- nounced, distribution was noted for attapulgite. The studies suggest that the minerals have developed authigenically in alkaline lacustrine environments during periods of desiccation. Such an environ- ment, interrupted by more humid periods, would have obtained during dry Pleistocene intervals. Volcanic ash is suggested as the source of the essential silica. The Mg concentration would appear to determine whether sepiolite-dolomite or attapulgite-calcite were formed.

Calcium-Magnesium Exchange in Montmorillonite and Vermiculite*

Abstract: An experimentally determined Ca-Mg exchange isotherm of montmorillonite is reported. The selectivity coefficient of this exchange over a wide range of Mg saturation was calculated and found constant. Standard free energies of exchange, thermodynamic equilibrium constants and activity coefficients of the exchangeable Ca and Mg ions in vermiculite and montmorillonite, were predicted from knowledge of the microstructure of these two clays, assuming that coulombic forces are the main ones playing a role in the interaction between the counterions and the charged clay surface. The standard free energies of exchange (ΔG° Ca Mg = 238 cal/mole) predicted a preference for Ca in montmorillonite and a preference for Mg in vermiculite (ΔS° Ca Mg = - 1665 cal/mole). The predicted thermodynamic equilibrium constants were compatible with the experimentally determined selectivity coefficients K sCa Mg = 0·67 as compared with K sCa Mg = 0·68 in montmorillonite, which remains constant over all the range of Mg saturation, and K Ca Mg = 16·7 as compared with K sCa Mg = 13·9 in vermiculite at 95% Mg saturation. The activity coefficients of Ca and Mg counterions in montmorillonite were found to be fCa = 2·0 × 10-3 and fMg = 2·2 × 10-3, respectively, and to remain constant. The activity coefficients of exchangeable Ca and Mg in vermiculite were found to be fCa = 7·1 × 10-5 and fMg = 3·5 × 10-5, respectively, at an equivalent fraction of unity. The activity coefficient of exchangeable Mg increased as the saturation with Mg decreased, and was found to be 1·7 × 10-3 in the range of the low Mg saturation. The microstructure, the isomorphic substitution and the surface charge density provided an understanding of the changes taking place in the activity coefficients of the counterions.

A sepiolite-rich playa deposit in southern nevada*

Abstract: Sepiolite is seldom reported in playa deposits, even though it is generally believed to form in a highly saline, alkaline environment. Its rareness suggests that unusual conditions are necessary for formation of sepiolite. Sepiolite is a major constituent of a near-surface playa bed 4 ft thick in the Amargosa Desert, southern Nye County, Nevada. Associated materials include dolomite and small to trace amounts of quartz, feldspar, montmorillonite, illite, and volcanic glass. The dolomite, averaging about 2μ in size, makes up about 40% of the bed. The overlying beds and the underlying ones down to a sampled depth of 13½ ft are montmorillonitic (saponite) clays with moderate to trace amounts of sepiolite; dolomite is abundant in all these clays except in the uppermost several feet, where calcite is a major constituent. Ground water in this area contains abundant magnesium compared with that in the rest of the Amargosa Desert. An initial high concentration of magnesium in the playa lake water probably promoted the development of sepiolite and dolomite. Concentration of dissolved salts through evaporation of water is believed to have started chemical precipitation of dolomite, and this precipitation and the continued evaporation later caused deposition of sepiolite.

Determination of chlorite compositions by x-ray spacings and intensities

Abstract: The cell dimensions and compositions of four chlorites whose crystal structures have been determined in detail are used to test existing graphs and regression equations designed to give tetrahedral and octahedral compositions. It is found that the thicknesses of the tetrahedral sheet, the 2:1 octahedral sheet, the interlayer sheet, and the space between the 2:1 layer and the interlayer can vary appreciably from specimen to specimen quite independently of tetrahedral composition. Total octahedral composition, the number of octahedral vacancies, cation ordering, and the distribution of trivalent cations and of charge between the two octahedral sheets must have effects on d(001) that are additional to the effect of tetrahedral composition. Nevertheless, Brindley’s d(001) graph and a regression equation by Kepezhinskas both should give tetrahedral compositions with an average error of 10%, or about 0·;1 AlIV, for most trioctahedral chlorites. They are not valid for dioctahedral or di, trioctahedral species. Equations derived from the data of von Engelhardt and of Shirozu relating the b parameter to octahedral Fe, Mn content give results with an average error of 10%, or 0·;1 Fe, Mn, for the four test chlorites provided Cr is included with the Fe, Mn, as does a regression equation by Kepezhinskas that contains terms for both the b parameter and d(001). Methods using the (00l) intensities or structure amplitudes give less consistent results for heavy atom contents than the spacing methods, but can be used to give approximate values for the asymmetry in distribution of heavy atoms between the 2:1 octahedral sheet and the interlayer.

Adsorption of Ethylenediamine (EDA) on Montmorillonite Saturated with Different Cations—II. Hydrogen- and Ethylenediammonium-Montmorillonite: Protonation and Hydrogen Bonding

Abstract: The form under which ethylenediamine (EDA) is adsorbed from aqueous solution by hydrogen- and ethylenediammonium-montmorillonite was studied as a function of the amount of amine present in the system. EDA added to the acid clay in quantities lower than or equal to the cation exchange capacity (C.E.C.) was exclusively adsorbed as ethylenediammonium (EDAH22+) ion. On further addition of diamine the pH of the suspension rose to alkaline values and the monoprotonated species (EDAH+) was the main charge balancing cation. Evaporating at room temperature “EDA-H-montmorillonite-H2O” or “EDA-EDAH2-mont- morillonite-H2O” systems containing 300 me EDA/100 g clay did not cause loss of nitrogen, but degassing under high vacuum (10−5 mm Hg) did. Nevertheless, excess EDA molecules with respect to the C.E.C. were retained on the clay surface, at the expense of water molecules, through strong asymmetrical hydrogen bonds between their NH2 groups and the NH3+ groups of EDAH+ ions. On heating up to 160°C under vacuum the nitrogen content decreased further, but still remained at a level significantly higher than the C.E.C. value, all NH3+ groups remaining involved in strong hydrogen bonding. It is suggested that a “condensation” process takes place, implying evolution of EDA molecules and giving rise to “polymeric” associations between protonated and unprotonated diamine. Washing the clay suspensions with distilled water did not completely remove excess EDA either, as a consequence of the equilibrium existing between the ionic species in solution (EDAH22+ and EDAH+) and on the clay surface. It seems that these species were preferentially adsorbed as “trimeric” associations in which two out of four NH3+ groups are hydrogen bonded to NH2 groups. After heating at 200°C, nitrogen retained on the clay surface was mainly in the form of NH4+ ions. Ammonium formation was enhanced by the presence of excess EDA and was considerably faster than in montmorillonite systems containing EDA coordinated to Cu2+ ions.

Laboratory alteration of trioctahedral micas

Abstract: Artificial alteration of thirty-five trioctahedral .and one dioctahedral micas by solutions varying in strength from 0.001 to 1.00 molal magnesium sulfate was found to approximate a normal exchange reaction after surface effects are eliminated. The equilibrium constants for the reaction: 1/2 Mg 2+ + K-mica = Mgv2-mica + K + (vermiculite) range from 0.0001 to 0.0028 and average 0.0010 in value. X-ray diffraction study reveals that iron-rich micas tend to develop a 1 : 1 mixed-layer biotite-vermiculite structure in weak magnesium sulfate solutions whereas magnesium-rich biotite and phlogopite alter to vermiculite. Mica composition also influences the degree of alteration of mica to vermiculite. High fluorine and octahedral multivalent cation contents tend to retard the reaction whereas high magnesium content and perhaps high calcium contents tend to favor the alteration. The equilibrium constant data indicate that vermiculite and hydrobiotite are more stable than trioctahedral micas in most weathering environments.

Comparative chemical composition of sediment interstitial waters

Abstract: Interstitial waters squeezed from modern sediments with a 100 psi pressure at laboratory temperature (23~ are depleted in K and Ca and enriched in Mg when compared to the solutions obtained at in situ temperature (28~ The changes are especially pronounced when the samples are refrigerated during transport back to the laboratory. The magnitude of the variation in chemical com- position was dependent on the element being analyzed as well as the sediment used. The maximum observed depletion in the laboratory was about 12% per degree difference in temperature for potas- sium. Element ratios in the solutions were affected most seriously. The Mg/Ca and Na/K ratios in- creased 51 and 60% respectively. A water extraction method using sediment to water ratios of 1 : 2, 1 : 5, and 1 : 10 was compared with the pressure method. The total composition of the pore fluids obtained by squeezing is greater than expected, corresponding to a sediment to water ratio less than 1 : 5. The artificially squeezed sediments are yielding pore fluids which are more concentrated than the "in-place" solutions. The water extraction method yields results which are in agreement with the behavior predicted by the Donnan Principle. It is suggested that the values obtained by successive dilution analyses can be extrapolated to measured moisture contents and used to determine the elemental composition and element ratios in interstitial pore fluids.

Alkylammonium Decomposition on Montmorillonite Surfaces in an Inert Atmosphere

Abstract: A study of the thermal transformation of alkylammonium cations adsorbed on the surface of a montmorillonite in various conditions of hydration has been carried out. The experimental conditions were: inert atmosphere, temperatures below 250°C and time periods up to 270 days. The reactions observed are mainly transalkylations, for which a mechanism of acid catalysis is proposed. A high degree of dissociation of the water remaining on the surface of the clay is required and is attained for an optimal, and rather low, water content of the clay.

Formation of an interstratified mineral by extraction of potassium from mica with sodium tetraphenylboron

Abstract: Interlayer K was extracted with sodium tetraphenylboron solution from a powdered sericite heated to the temperature of dehydroxylation and quenched to room temperature. By this procedure, sericite of the 2M1 type was changed to an interstratified mineral. The X-ray diffraction properties of this interstratified mineral are similar to ‘rectorite’.

Reactions between Fulvic Acid and Cu2+-Montmorillonite*

Abstract: Shaking of water-soluble fulvic acid with Cu2+-montmorillonite at pH 2·;5 increased the interlamellar spacing from 10·;0 to 15·;1 A. The spacings were measured at ≈0% relative humidity. The extent of interlayer adsorption decreased with increase in pH. Differential thermal analysis and thermogravimetric examinations showed that in addition to interlayer adsorption, fulvic acid was also retained on external clay surfaces. The FA was held so tightly by the Cu2+-clay that > 3/4 of the total amount adsorbed, including degradation products formed from it, resisted decomposition even when heated to 1000°C. I.R. spectra showed that β-diketone groups in fulvic acid reacted with Cu2+ in or on the clay to form acetylacetonate-type chelates. Indications were obtained that the mechanism postulated for the FA-Cu2+-clay interaction may also apply to reactions between FA and montmorillonite saturated with other di- and trivalent metal ions. Reactions of FA in aqueous solutions with metal ions in the presence of clays differ from those in the absence of clay. Montmorillonite appears to affect the conformation of the fulvic acid polymer in a way that favours reactions between C=O groups and metal ions, a type of reaction that has so far not been observed in aqueous solutions in the absence of clay.

Acid-base interactions and the properties of kaolinite in non-aqueous media

Abstract: In non-aqueous systems, kaolinite can show, in addition to the physical interactions, considerable chemical activity. This study considers the chemical reactions that can occur at the kaolinite surface and explains these reactions in terms of acid-base interactions. In certain applications the chemical activity must be controlled if satisfactory products are to be obtained; for example, when kaolinite is used as a filler in rubber or as a diluent for insecticide powders. The concept of acid-base interactions is used to explain rheological and film properties in kaolinite-organic systems. The strength of the surface acid sites of kaolinite varies with the moisture content. At 1% moisture the surface is equivalent to 48% sulphuric acid whereas at 0% it is equivalent to 90% sulphuric acid. Therefore, the moisture level is extremely important and dry kaolinite will promote or catalyze many chemical reactions and where acid-base interactions are involved the presence of even small amounts of water usually retards or inhibits the reaction. Several examples explaining these interactions are given in the paper.RésuméDans les systèmes non aqueux, la kaolinite peut montrer, en plus des interactions physiques, une activité chimique considérable. Ce travail se rapporte aux réactions chimiques qui peuvent se produire à la surface de la kaolinite, et explique ces réactions en termes d’interactions acide-base. Dans certaines applications, l’activité chimique doit être contrôlée si l’on désire obtenir des produits satisfaisants; c’est le cas par exemple, lorsque la kaolinite est utilisée comme charge minérale dans le caoutchouc ou comme diluant dans les poudres insecticides. Le concept d’interactions acide-base est utilisé pour expliquer les propriétés rhéologiques et de films dans les systèmes kaolinite-produit organique. La force des sites acides de surface de la kaolinite varie avec la teneur en eau. A une humidité de 1% la surface est équivalente à de l’acide sulfurique à 48%, alors qu’à 0% d’eau, elle est équivalente à da l’acide sulfurique à 90%. Ainsi, le taux d’humidité est extrêmement important et de la kaolinite sèche facilitera ou catalysera de nombreuses réactions chimiques; lorsque des interactions acide-base sont en cause, la présence d’eau, même en quantité très faible, retarde ou inhibe en général la réaction. Plusieurs exemples expliquant ces interactions sont donnés dans cet article.KurzreferatIn nicht-wässrigen Systemen kann Kaolinit, zusätzlich zu den physikalischen Wechselwirkungen, beträchtliche chemische Aktivität aufweisen. In dieser Arbeit werden die chemischen Reaktionen betrachtet, die an der Oberfläche des Kaolinits stattfinden können, und diese Reaktionen durch Säure-Base Wechselwirkungen erklärt. In gewissen Anwendungsgebieten muss die chemische Aktivität gesteuert werden wenn befriedigende Produkte erhalten werden sollen, zum Beispiel, wenn Kaolinit als Füllmaterial in Gummi oder als Verdünnungsmittel für insektentötende Pulver verwendet wird. Der Begriif der Säure-Base Wechselwirkungen wird verwendet um die Theologischen und Filmeigenschaften in kaolinitorganischen Systemen zu erklären. Die Stärke der Säurestellen an der Oberfläche von Kaolinit variiert mit dem Feuchtigkeitsgehalt. Bei 1% Feuchtigkeit entspricht die Oberfläche 48% Schwefelsäure während sie bei 0% einer Stärke von 90% Schwefelsäure entspricht. Das Feuchtigkeitsniveau ist daher äusserst wichtig und wenn en sich un Säure-Base Wechselwirkungen handelt kann die Gegenwart auch kleinster Mengen von Wasser die Reaktion verlangsamen oder sogar verhindern. In diesem Artikel werden verschiedene Beispiele angeführt, die diese Wechselwirkungen veranschaulichen.РезюмеВ безводных системах каолинит проявляет, кроме физических взаимодействий, значительную химическую активность. Настоящая работа рассматривает происходящие на поверхности каолинита химические реакции и объясняет их в терминах взаимодействия кислот и оснований. Если требуется получить для некоторых применений удовлетворительные продукты, то химическую активность надо контролировать; например, когда каолинит используется в качестве наполнителя для резины или как растворитель для порошкообразных инсектицидов. Принцип взаимодействия кислот/оснований применяется для объяснения реологических и пленочных свойств каолинитных органических систем. Прочность кислотных сторон поверхности каолинита изменяется с изменением влагосодержания. При 1 % влажности поверхность эквивалентна 48%—ной серной кислоте, а при 0% эквивалентна 90%—ной серной кислоте. Поэтому, уровень влажности чрезвычайно важен и сухой каолинит может быть катализатором многих химических реакций и ускорять их, а где происходит взаимодействие кислот-оснований, присутствие даже малых количеств воды обычно замедляет или тормозит реакцию. В статье приводятся несколько примеров, объясняющих эти взаимодействия.

Zeolite as Catalysts for the Synthesis of Amino Acids and Purines

Abstract: This paper attempts to show that the catalytic properties of zeolitic material may play a role in the synthesis of simple biological molecules from gases commonly found in extraterrestrial atmospheres. Linde X and Y molecular sieves cation-exchanged by Ca2+ and Fe3+ have been heated in the presence of carbon monoxide and ammonia. Amino-acids and u.v. absorbing substances identified by paper chromatography have been extracted from the solid. HCN, the basic molecule involved in the synthesis of those substances has been detected in the gas phase. It is proposed, on the basis of i.r. results, that the amino-acids are hydrolysis products of an undefined polymer.

X-Ray Diffraction and Electron Optical Studies on Smectite and α -Cristobalite Associations

Abstract: Alteration products of volcanic materials from various localities in Wyoming, U.S.A., Italy, Yugoslavia and Mozambique are mainly smectites and cristobalites with small amounts of kaolinite. Smectite and cristobalite form separate and intergrown aggregates of microcristallinity. X-ray diffraction studies show that the silica is a-cristobalite with a noticeable stacking disorder. Small aggregates of optically pure o~-cristobalite, which were separated by an appropriate mixture ofbromo- form and carbon tetrachloride, are shown to contain a noticeable amount of smectite on Debye- Scherrer diffraction photographs for the samples from Italy and Wyoming, U.S.A. Transmission electron micrographs and selected area electron diffraction photographs show, in addition to smectite and c~-cristobalite aggregates, the presence ofidiomorph single crystals of kaolinite.

The I.R. Spectra of Lysine Adsorbed on Several Cation-Substituted Montmorillonites

Abstract: The i.r. spectra (4000-1200 cm 1) are obtained for several cation-substituted-montmorll- lonite-lysine complexes that were prepared at their natural pH's. Analyses of the spectra of copper-, cobalt-, nickel- and zinc-montmorillonite films indicate that bidentate chelate complexes which contain protonated e-amino-groups are present in the interlamellar spaces. Investigation of the spectra of the hydrogen-, calcium- and natural-montmorillonite films indicates that the dominant adsorbed species for these complexes is a lysine cation in which both the c~- and the e-amino-groups are protonated while the carboxyl group is ionized.

Irreversible Collapse of Montmorillonite

Abstract: A number of variable charge montmorillonites were prepared. One portion of each sample was extracted with ammonium chloride, while a second portion was first saturated with calcium chloride, washed, and then extracted with ammonium chloride. In both cases, the number of cations displaced by ammonium chloride was determined. The number of calcium ions displaced from Ca-saturated samples was higher than the sum of the number of lithium and calcium ions displaced from Li, Ca-mixed samples. The differences, increasing towards Li-rich end of the series are assumed to be due to protons liberated from the reaction of lithium ions with either structural hydroxyl groups or residual water molecules, as has been shown by other investigators. Supplementary X-ray and i.r. data lend support to this idea.

Some effects of grinding kaolinite with potassium bromide

Abstract: to be quite compatible with the original analytical scheme. Incidentally, El-Attar and Jackson (1973) have observed considerable thermal decomposition at 550~ of Fe-rich layers and/or interlayers in montmorillonitic soils of Nile River alluvium. Additional information that can be deduced from the above procedure is the CEC and K § -fixation capacity of the amorphous constituents of the clays provided these values are determined for the original clays also. The present modification avoids the assignment of arbitrary, possibly erroneous, values of CEC and K+-fixation capacity values to the amorphous inorganic constituents of soil clays.

Transmission Electron Microscopy of Fine-Grained Phyllosilicates in Ultra-Thin Rock Sections

Abstract: A method is described for preparing electron-transparent sections of fine-grained argillaceous rocks suitable for making transmission micrographs. A sediment and a slate are used as examples. Sections perpendicular to bedding or cleavage yield diffraction patterns with clearly defined 00l reflections. These allow immediate identification of 7, 10 and 14 A structures. The combination of detailed textural information with structural identification of individual phyllosilicate particles affords a powerful method for the investigation of late diagenetic and early metamorphic changes in sediments.

Swelling Characteristics of Hydroxy-Aluminum Interlayered Clays*

Abstract: The hypothesis tested was that macroscopic swelling of montmorillonitic clays is reduced by the presence of interlayer minerals. Fine and coarse clay fractions of Camargo and Panther Greek bentonite samples were artificially interlayered by reaction of A12(SO4)3 and NaOH in 0∙5% suspensions of the clays. All four clay fractions reacted similarly to artificial interlayering. At an Al:clay ratio of 16 meq Al/g clay the CEC was completely lost, surface area was reduced and X-ray basal spacings were altered. No macroscopic swelling occurred in samples treated with 16 meq of Al/g of clay. At smaller concentrations of hydroxy-aluminum 8 and 2 meq Al/g clay, the clay properties were less drastically altered. Extraction of interlayered clays with Na citrate restored the original C.E.C., surface area, and basal spacings of all samples and resulted in some slight enhancement of C.E.C. and surface areas of the coarse fractions. Treatment with hot Na citrate resulted in an increase in swelling ability but only slight increases in C.E.C. and surface area. Evidence presented supports the hypothesis that macroscopic swelling of montmorillonitic clays is greatly reduced by interlayer materials. Reduced swelling due to interlayering occurs even when other clay properties may be slightly different from those of nontreated samples. Indications are that interlayer material occurs naturally in the clays studied and this may apply to other bentonite deposits.