The nature of clay volatiles and condensates and the effect on their environment

When clays are heated, a mass loss occurs due to the evolution of volatiles. Most of these are water vapour, but in addition minor amounts of a complex assemblage of other species are liberated. The corresponding condensates are colloidal suspensions. The composition of the volatiles and condensates and the release patterns of the gases are reviewed. The nature of the assemblages varies from one clay to another and depends on the thermal regime. Both volatiles and condensates are very reactive. Their reactivity persists even after prolonged storage. They act as acid catalysts in reactions with organic matter and decompose calcite and other carbonates. Condensates were found to etch the surfaces of quartz crystals and to dealuminate and partly destroy an Al-rich faujasite (zeolite). Possible implications of reactions of clay volatiles and condensates for natural processes are discussed.     

Effect of temperature on the conformation of dibenzotropone adsorbed on montmorillonites

The nature of the adsorption complex formed between dibenzotropone (DBT) and montmorillonite at elevated temperatures is strongly dependent on the interlayer cations. This was shown by electronic and IR spectra, by X-ray diffraction, and by study of the effects of gradual heating of the samples on these analyses. All samples exhibited significant red shifts of the electronic spectra of DBT into the visible range. These red shifts are attributed to two factors, both contributing to the enhancement of the tropylium planar character of DBT: hydrogen-bonding of acidic interlayer water to the carbonyl group, imparting positive charge to the tropone ring; and π interactions between the aromatic moiety and the oxygen planes. The position of the maximum was temperature-dependent for Cu-, Ni-, Al- and Fe-montmorillonites, for which heating (100°) under vacuum increased the red shift. The organic molecule assumes a planar conformation and is oriented parallel to the clay layers. IR spectra confirming this conformational orientation of DBT are discussed. The basal spacings of the DBT montmorillonite associations depend on the number of water and DBT sheets present in the interlayers. Layers with one or two sheets of DBT and with up to two sheets of water could be distinguished, leading to a maximum spacing of 20.4 Å.     

Thermal reactions of kaolinite with potassium carbonate

It was previously established that kaolinite reacts with K₂CO₃ on heating to form products of KSiAlO4 composition. In the present study we investigated the solid state reactions with K₂CO₃ of four kaolinites of different thermal stability. The mixtures were calcined at temperatures ranging from 400-700°C and washed before or after boiling with the remaining K₂CO₃. FTIR spectra indicated that the X-ray amorphous material formed after calcining the mixtures at 500-590°C had a SiAlO₄ tetrahedral framework. Attempts to convert the products to zeolites gave promising results. After calcining at 700°C under atmospheric pressure synthetic kaliophilite (KSiAlO₄) was obtained. These conditions are appreciably milder than previously reported for kaliophilite syntheses. Conversion to kalsilite increased with decreasing thermal stability of the original kaolinite. In similar reactions with KCl much less K was incorporated into the amorphous phase and kaliophilite was not obtained. The reactions of the four kaolinites with K₂CO₃ or with KCl were similar in trend, but differed in detail. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mineral reactions and pyrolysis of Israeli oil shale

The mineral reactions of Israeli oil shale fed to the GENESIS ($\text{G}$eneration of $\text{Ene}$rgy from $\text{S}$hale of $\text{Is}$rael) split-stage fluidized-bed reactor have been studied by infrared. X-ray and chemical means. Organically bonded sulphur released during pyrolysis reacts with oxygen from the fluidizing air and with CaO resulting from decomposition of calcite to form CaSO₄, mostly in a surface layer. At pyrolysis and coke-oxidation temperatures near 600°C, kaolinite reacts with calcite to form amorphous modified metakaolinite. At organic gas combustion temperatures near 1000°C, the amorphous phase in overhead fines reacts with additional calcite and quartz to yield gehlenite and larnite.     

Novel features of smectite settling

Aqueous suspensions of Ca or Mn montmorillonite were left to settle in cylinders ranging in diameter, D, from 1.0 to 7.7 cm after magnetic stirring and/or manual tumbling. Changes in height, H, of the interface between the turbid suspension and the clear supernatant were recorded visually as a function of time, T. In the absence of added electrolytes the H/T plots were approximately linear, but after addition of electrolytes they assumed an inverse S shape. An initial latency period was followed by a time of rapid settling and, finally, by slow compaction of the sediment until no further changes occurred. Within a limited range of concentration the latency period increased exponentially with decreasing D. It increased with increasing height of the settling columns, H_i, and with increasing concentration of the suspensions. With Mn montmorillonite the rate of fast settling also depended on D. The parameters of the H/T plots depended on the prehistory of the samples. Fairly reproducible results were obtained in duplicates within any one series of experiments, but changes in the pretreatment altered the parameters. Treatment of the suspensions with an ultrasonic tip changed the settling process drastically. Sedimentation became very slow, the effects of D and H_i on the latency period were reversed and the final sediment volume increased. The effects of vessel diameter on sedimentation observed are much greater than any wall effects described in the literature. The changes observed after ultrasonication of the suspensions, particularly the reversal of the effects of D and H_i on the settling process, are novel features.     

Thermal analysis of the interaction between stearic acid and pyrophillite or talc. IR and DTA studies

Pyrophyllite and talc sorb stearic acid on edge surfaces. The grinding of clay-stearic acid associations in the presence of alkali halides converts some of the acid into the ionic form, this occurring more readily with talc than with pyrophyllite. Heating in a closed or semi-closed system causes dissociation of stearic acid adsorbed on talc, but not on pyrophyllite. The infrared absorption frequencies of the adsorbed ionic form vary with the clay mineral and the amount of water present. The thermal stabilities of the clay-stearic acid associations depend on the rate of escape of the acid, which is determined by the strength of bonding to the clay and the nature of the system, and on the degree of dissociation of the acid on the clay surfaces.

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Zusammenfassung Pyrophyllit und Talk adsorbieren Stearinsäure an den Kantenoberflächen. Beim Verreiben von Ton-Stearinsäure-Assoziaten in Gegenwart von Alkalihaliden wird ein Teil der Säure in die ionische Form überführt, und zwar leichter mit Talk als mit Pyrophyllit. Aufheizen im geschlossenen oder halbgeschlossenen System bewirkt eine Dissoziation der an Talk, aber nicht der an Pyrophyllit adsorbierten Stearinsäure. IR-Absorptionsfrequenzen der adsorbierten ionischen Form sind abhängig vom Tonmineral und der anwesenden Wassermenge. Die thermische Stabilität der Ton-Stearinsäure-Assoziate hängt von der Geschwindigkeit der Abgabe der Säure ab, die durch die Stärke der Bindung an das Tonmineral, also der Natur des Systems, und durch den Dissoziationsgrad der Säure an der Tonmineraloberfläche bedingt ist.

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