Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different micro-structure constitution. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge-to-face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.     

Intercalation of cyclic imides in kaolinite

The intercalation of two cyclic imides, succinimide and glutarimide, in the interlayer spaces of kaolinite was obtained from a "soft guest-displacement method" by displacing previously intercalated guest molecules. The dimethyl sulfoxide (DMSO)-kaolinite preintercalate was particularly efficient for that purpose. The intercalation exchange was done from a concentrated aqueous solution of the cyclic imides, at ambient temperature, in a relatively short time. Complete displacement of DMSO by the cyclic imides was confirmed by the results of several independent characterizations, including XRD, TG/DTA, FTIR, and (13)C MAS NMR analyses including dipolar dephasing experiments. The imide intercalates are two dimensionally constrained in the kaolinite interlayer spaces, and are structurally organized in a flattened configuration with their cycle roughly parallel to the ab plane of the kaolinite layers. Elemental analysis gives the following compositions: Al(2)Si(2)O(5)(OH)(4)(C(4)H(5)NO(2))(0.65) and Al(2)Si(2)O(5)(OH)(4)(C(5)H(7)NO(2))(0.49), respectively for succinimide and glutarimide. The results of the TG/DTA analyses showed enhanced thermal stabilities of the imide intercalates compared with the starting materials. The intercalation process from the aqueous solution is reversible: in prolonged contact with water, the imide molecules are released, resulting in the rebuilding of the kaolinite structure. These results demonstrate the potential use of kaolinite as a slow-releasing agent for molecules structurally related to the cyclic imides of this study.     

Modification of low- and high-defect kaolinite surfaces: implications for kaolinite mineral processing

A comparison is made of the mechanochemical activation of three low- and one high-defect kaolinite using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. The effect of mechanochemical alteration of the kaolinites is greater for the low-defect kaolinites. The effectiveness of the mechanochemical treatment is represented by the slope of the d(001) peakwidth-grinding time line. High-defect kaolinite is not significantly altered by the grinding treatment. The effect of mechanochemical treatment on peakwidth was independent of the presence of quartz; the quartz acts as an additional grinding medium. The effectiveness of the mechanochemical treatment depends on the crystallinity of the kaolinite. Two processes are identified in the mechanochemical activation of the kaolinite: first the delamination of kaolinite appears to take place in the first hour of grinding and second a recombination process results in the reaggregation of the ground crystals. During this process proton hopping occurs and reaction to form water takes place. This water is then adsorbed and coordinated to surface-active sites created during mechanochemical treatment.     

Dehydroxylation of kaolinite group minerals

The kinetics of dehydroxylation of kaolinite and halloysite have been tested by the methods of thermal analysis. They are determined by the particle sizes of these minerals and the order of stacking of the layers in their structures. The Arrhenius activation energyE and order of reactionn decrease with the increase in specific surface area of the minerals. An increase in the degree of disorder of the kaolinite lattice diminishes the value ofE. It also influences then value for fractions finer than 1m.

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Zusammenfassung Die Kinetik der Dehydroxylierung von Kaolinit und Halloysit wurde durch Methoden der Thermoanalyse geprüft. Die Bestimmungen erfolgten über die Teilchengrösse dieser Mineralien und die Reihenfolge der AnhÄufung der Schichten in ihrer Struktur. Die AktivierungsenergieE nach Arrhenius und die Reaktionsordnung nehmen mit zunehmender spezifischer OberflÄche der Minerale ab. Die Zunahme des Grades der Unordnung des Kaolinitgitters setzt den Wert vonE herab. Sie beeinflusst auch den Wertn der Fraktionen feiner als 1m.

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Résumé On a étudié par les méthodes de l'analyse thermique, la cinétique de déshydroxylation de la kaolinite et de l'halloysite. Les déterminations ont été effectuées à partir de la taille des particules de ces minéraux et de l'ordre d'empilement des couches dans leur structure. L'énergie d'activationE d'après Arrhénius et l'ordre de réaction diminuent avec l'augmentation de la surface spécifique des minéraux. L'augmentation du degré de désordre du réseau de la kaolinite diminue la valeur deE. Elle influence de mÊme la valeurn des fractions inférieures à 1m.

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. . E . E. n 1.

     

ESR spectra of oxygen radical-ions in kaolinite

V. V. Kuibyshev Novosibirsk Construction Engineering Institute and Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 1, pp. 171–173, January–February, 1992.     

The surface energy of kaolinite

The surface energy of kaolinite was determined from the water adsorption isotherm, the water/kaolinite contact angle, and the surface tension of water, using a formula obtained by combining the Young equation with the general equation of pair interaction. This formula could be represented by a polynomial function whose roots gave one real value of 252.57±2.75 mJ m^–2 for the surface energy of kaolinite. An important feature of the procedure for obtaining this energy is the use of the Young equation to determine the range in which the value of the surface energy lies.     

Adsorption of polyvinylimidazole onto kaolinite

The adsorption of polyvinylimidazole (PVI) onto kaolinite from aqueous solutions has been investigated systematically as a function of parameters such as calcination temperature of kaolinite, pH, ionic strength, and temperature. According to the experimental results, the adsorption of PVI increases with pH from 8.50 to 11.50, temperature from 25 to 55 degrees C, and ionic strength from 0 to 0.1 mol L(-1). The kaolinite sample calcined at 600 degrees C has a maximum adsorption capacity. Adsorption isotherms of PVI onto kaolinite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. Furthermore, the zeta potentials of kaolinite suspensions have been measured in aqueous solutions of different PVI concentrations and pH. From the experimental results, (i) pH strongly alters the zeta potential of kaolinite; (ii) kaolinite has an isoelectric point at about pH 2.35 in water and about pH 8.75 in 249.9 ppm PVI concentration; (iii) PVI changes the interface charge from negative to positive for kaolinite. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. The dimensionless separation factor (RL) has shown that kaolinite can be used for adsorption of PVI from aqueous solutions.     

Modification of kaolinite with alkylimidazolium salts

We have demonstrated that the d-spacing and thermal stability of the alkylimidazolium intercalated kaolinite compounds can be controlled by adjusting chain length of the alkyl groups. The composites were synthesized by displacement method using selected imidazolium ionic liquids bearing different short alkyl chains as guest molecules. The effects of the length of alkyl side chain on d-spacing and thermal stability of the ionic liquids–kaolinite intercalations were investigated by XRD and TG-DSC. Results revealed that in these composites, increasing the length of alkyl substituent led to larger d-spacing and decreased thermal stability. Temperature was found to have influence on the intercalation ratio but not on the d-spacing of final product. The present study shows an easy way of tailoring the performance of these intercalations via small variation of guest ionic liquids, providing the possibility of finding “species-specific” modifier for fully exfoliated nanocomposites.     

Sintering of kaolinite with ammonium fluoride

The present work represents a study of the influence of ammonium fluoride on the thermal behaviour of kaolinite by using a derivatograph. The sintering of kaolinite with ammonium fluoride was found to be complicated. Different products of sintering are obtained, depending on the temperature and the amount of ammonium fluoride. They were identified microscopically and by using a Siemens Crystalloflex diffratometer. These include an ammonium aluminium fluoride complex, cryptohalite, aluminium fluoride, mullite, topaz and corundum. The DTA curves (using kaolinite and ammonium fluoride mixes of ratio 1:1) indicate the formation of the ammonium aluminum fluoride complex and cryptohalite at 120–280°C and the appearance of aluminium fluoride, topaz and mullite at 640°C. The intensive formation of topaz takes place at 750°C and its subsequent dissociation at 940°C with corundum formation. The very small endothermic peak at 1010°C represents the formation of mullite. In experiments using mixes of kaolinite—ammonium fluoride in the ratios 1:1 and 1:1.3 the end-product of sintering consists of corundum and mullite. When using mixes of the ratio 1:1.7, aluminium fluoride constitutes the main composition of the end-product.     

Adsorption of aspartic acid on kaolinite

The interaction of aspartic acid with kaolinite was studied by potentiometric titrations and by adsorption measurements both at constant aspartate concentration (but varying pH) and at a constant pH of 5.5. The temperature was 25 degrees C, and the ionic medium 5 mM KNO3. Aspartic acid dissociation constants estimated from titrations agreed with those from the literature. The adsorption of aspartic acid to kaolinite was weak and varied only slightly with pH; 10-18% of 100 microM aspartic acid adsorbed to kaolinite at 100 m(2)L(-1) between pH 3 and 10. Data from the titrations and adsorption experiments were fitted closely by an extended constant-capacitance surface complexation model, in which monodentate outer-sphere complexes formed between deprotonated aspartic acid molecules and protonated sites on the variable-charge edges of the kaolinite crystals. There appeared to be no adsorption to the permanently charged crystal faces.     

Thermal decompositions of kaolinite intercalation compounds

Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.Decomposition of the potassium acetate intercalation compound proceeds simultaneously with the dehydroxylation of kaolinite at an extrapolated onset temperature of 360 °C. The high-temperature reactions (dehydroxylation and transformation) of kaolinite obtained through the decomposition of intercalation compounds with volatile intercalation agents depend on the conditions applied during decomposition.

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Zusammenfassung Mittels Röntgenbeugung und thermischer Analyse (simultane TG-DTG-DTA und quasi-isotherme-quasi-isobare TG) konnte gezeigt werden, daß das molare Verhältnis Einlagerungsmedium/Kaolinit in allen Einlagerungsverbindungen etwa 1 ist. In gesättigter Atmosphäre des jeweiligen Einlagerungsmediums ist die Einlagerungsverbindung stabil bis über 150 °C. Die Zersetzung der Kaliumacetat-Einlagerungsverbindung läuft zusammen mit der Dehydroxylation des Kaolinits bei einer extrapolierten onset-Temperatur von 360 °C ab. Die Hochtemperaturreaktionen (Dehydroxylation, Phasenneubildung) von Kaolinit, der aus der Zersetzung von Einlagerungsverbindungen mit flüchtigen Einlagerungsmedien erhalten würde, werden von den Zersetzungsbedingungen beeinflußt.

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- ( , , ) , - 1. , , 150°. — ** 360°, ** . , , .

     

Significance of structural factors in dehydroxylation of kaolinite polytypes

The relations between the perfection of the structure, the size of the crystals and the course of dehydroxylation of kaolinite polytypes, as revealed by DTA and DTG curves, are discussed. The dehydroxylation of kaolinites is a peculiar type of homogeneous, intracrystal thermal dissociation. The kinetics of this process are dependent on the rate of removal of water vapour from the structure and its pressure in the structural domains.

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Zusammenfassung Beziehungen zwischen dem Ordnungsgrad der Struktur, der Kristallgrö\e und dem durch DTA und DTG verfolgten Verlauf der Dehydroxylierung von Kaolinit-Polytypen werden diskutiert. Die Dehydroxylierung von Kaolinit ist ein besonderer Typ einer homogenen, intrakristallinen thermischen Dissoziation. Die Kinetik dieses Prozesses ist von der Geschwindigkeit der Entfernung des Wasserdampfes aus der Struktur der Probe, also vom Wasserdampfpartialdruck in der Probe abhÄngig.

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, , . , . .

     

Thermal analysis of dehydroxylation of Algerian kaolinite

Thermal analysis techniques remain important tools amongst the large variety of methods used for analysis of the dehydroxylation of kaolinite. In the present study, the kinetics of dehydroxylation of Algerian kaolinite, wet ball milled for 5 h followed by attrition milling for 1 h, was investigated using differential thermal analysis (DTA) and thermogravimetry (TG). Experiments were carried out between room temperature and 1350 °C at heating rates of 5, 10 and 20 °C min⁻¹. The temperature of dehydroxylation was found to be around 509 °C. The activation energy and frequency parameter evaluated through isothermal DTA treatment were 174.69 kJ mol⁻¹ and 2.68 × 10⁹ s⁻¹, respectively. The activation energies evaluated through non-isothermal DTA and TG treatments were 177.32 and 177.75 kJ mol⁻¹, respectively. Growth morphology parameters n and m were found to be almost equal to 1.5.     

Particle interactions and rheological effects in kaolinite suspensions

Particle interactions in kaolinite suspensions are modelled by representing the edge face of a kaolinite platelet as cylinder and flat plate, respectively. Computations of total energy of interaction show that at pH 6,7 and 8 and in the presence of 10^?4 ?10^?I M NaCl both face-edge and edge-edge modes of interaction are likely. Rheological parameters for flocculated suspensions (extrapolated shear stress and plastic viscosity) for dilute sodium kaolinite suspensions (volumetric concentration 0.02) are interpreted in terms of the proposed interaction models.     

Preferred conformers of proteinogenic glutamic acid

The molecular shape of proteinogenic glutamic acid has been determined for the first time. Vaporization of the solid amino acid by laser ablation in combination with Fourier transform microwave spectroscopy made possible the detection of five different structures in a supersonic jet. These structures have been identified through their rotational and (14)N quadrupole coupling constants. All conformers show hydrogen bonds linking the amino and alpha carboxylic group through N-H···O═C (type I) or N···H-O (type II) interactions. In three of them there are additional hydrogen bonds established between the amino group and the carboxylic group in the gamma position. Entropic effects related to the side chain have been found to be significant in determining the most populated conformations.     

Identification of superactive centers in thermally treated formamide-intercalated kaolinite

The thermal behavior of a formamide-intercalated mechanochemically activated (dry-ground) kaolinite was investigated by thermogravimetry-mass spectrometry (TG-MS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). After the removal of adsorbed and intercalated formamide, a third type of bonded reagent was identified in the temperature range 230-350 degrees C decomposing in situ to CO and NH3. The presence of formamide decomposition products, as well as CO2 and various carbonates identified by DRIFT spectroscopy, indicates the formation of superactive centers as a result of mechanochemical activation and heat treatment (thermal deintercalation). The structural variance of surface species decreases with the increase of grinding time. The unground mineral contains a small amount of weakly acidic and basic centers. After 3 h of grinding, the number of acidic centers increases significantly, while on further grinding the superactive centers show increased basicity. With the increase of grinding time and treatment temperature the number of bicarbonate- and bidentate-type structures decreases in favor of the carboxylate- and monodentate-type ones.     

Deintercalation of hydrazine-intercalated kaolinite in dry and moist air

The deintercalation of hydrazine-intercalated kaolinite has been followed using a combination of X-ray diffraction and diffuse reflectance Fourier transform infrared spectroscopy. Upon intercalation of the kaolinite with hydrazine, the kaolinite layers are expanded to 10.66 A and remain expanded for up to 22 h upon exposure to moist air. Only upon deintercalation are the peak at 10.39 A and a minor peak at 9.6 A observed. Complete deintercalation takes up to 18 days more. Upon intercalation with hydrazine an intense band is observed at 3628 cm(-1) and is attributed to the inner-surface hydroxyls hydrogen bonded to the hydrazine, which upon deintercalation decreased in intensity. This rate of deintercalation is affected by the presence or absence of moist air. Deintercalation in the presence of water vapor results in the observation of two additional bands at 3550 and 3598 cm(-1), which are attributed to the hydroxyl stretching modes of adsorbed water during deintercalation. The intensity of NH stretching vibrations observed at 3360, 3300, and 3200 cm(-1) also decrease in intensity with deintercalation time. Changes in the hydroxyl deformation modes of kaolinite in the 915 cm(-1) region and in the HNH deformation modes show strong interactions between the kaolinite surface and the inserting hydrazine molecule.     

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.