S. Yariv

Organo-clay complexes and interactions

Structure and surface acidity of clay minerals introduction to organo-clay complexes and interactions interactions of vermiculites with organic compounds organophilicity and hydrophobicity of organo-clays adsorption of organic cations on clays - experimental results and modelling nuclear magnetic resonance spectroscopy thermal analysis of organo-clay complexes IR-spectroscopy and thermo-IR-spectroscopy in the study of the fine structure of organo-clay complexes staining of clay minerals and visible-absorption spectroscopy of dye-dye complexes clay catalysis in reactions of organic matter organo-materials and organo-clay interactions and the origin of life on Earth.

Wettability of Clay Minerals

Clay minerals, hydrated oxides, and hydroxides, mainly of Si, Al, Fe, and Mn, and some organic macromolecules are responsible for most wettability properties of geologic systems that constitute the sedimentary cycle. They are the soil components that exert the dominant influence on chemical and physical properties of a soil, and a detailed examination of the nature of their wettability by water is essential for a complete understanding of a soil’s potential with respect to agricultural and engineering applications.(1–3) The clay minerals, which generally constitute the greatest part of the colloid fraction in these systems, are named after the term used by sedimentologists and soil scientists for the fraction of particles having a very small size, with an equivalent diameter smaller than 2 μm, the “clay fraction.” Although most clay minerals occur as particles too small to be resolved by the ordinary microscope, x-ray diffraction analysis shows that most of them, even in their finest size fraction, are composed of crystalline particles and that the number of crystalline minerals likely to be found is limited. Furthermore, a wide distribution of particle size is frequently present and certain clay deposits contain well-defined crystalline particles with diameter greater than 2 μm.

The effect of tetrahedral substitution of Si by Al on the surface acidity of the oxygen plane of clay minerals

Abstract Oxygen planes of clay minerals are formed by a continuous linkage of [SiO4]4- tetrahedra. This plane determines many of the clay colloidal and surface properties. The dπ-pπ bond between O and Si in Si-O-Si and Si-O-Al groups is described here according to the valence bond treatment. Partial π interaction between O and Si causes the O atom to serve as a weak base. Tetrahedral substitution of Si by Al leads to changes in the clay surface properties, resulting from an increase in the basic strength of the siloxanes. Substitution of Mg by Al in octahedral sheets increases the polarization of the OH planes. Interlayer hydrogen bonds between oxygens and hydroxyls were detected in substituted serpentines and chlorites. Wettability of tetrahedral-octahedral-tetrahedral (TOT) clay minerals was determined from advancing contact angles of water. This angle decreased with increasing degree of tetrahedral substitution, indicating an increase in strength of hydrogen bonds between water and the oxygen plane, du...

Thermo-IR-spectroscopy analysis of the interactions between organic pollutants and clay minerals

A short description of thermo-IR-spectroscopy analysis is given together with some examples of the interactions between hazardous organic pollutants and clay minerals. Self-supported films of organo-montmorillonite and laponite complexes can be heated in a vacuum cell and the IR spectra of the samples recorded at different temperatures. Organo complexes of other clay minerals can be heated as alkali-halide disks. In this case the effect of the alkali halides on the stability of the organo-clays and on thermal reactions should be taken into consideration. This method is useful for determination of the fine structures of organo-clay complexes. It can be applied to obtain information on the adsorption mechanism of organic pollutants by clay minerals and on the types of bond which are obtained between adsorbed hazardous species and functional sites on the clay surfaces.

Infrared study of the thermal treatment of sepiolite and palygorskite saturated with organic amines

Abstract Butylamine (BA), pyridine (PY) and 2,4,6-trimethylpyridine (TMP) were adsorbed by sepiolite and palygorskite under reflux. The adsorption and the thermal stability of the organo-clay complexes were studied by IR thermospectrometry. In this technique KBr disks of the organo-clay complexes were heated to 100, 200, 300 and 400°C and IR spectra were recorded after each thermal treatment. The spectra proved that the adsorbed amines were located in the channels, replacing part of the zeolitic and bound water. The three amines were hydrogen bonded to the zeolitic water, Associations were also obtained between BA or PY and bound water in sepiolite but not in palygorskite and not with TMP. Small amounts of adsorbed BA and TMP were protonated. During the thermal treatment of the organo-clay, associations were formed between BA or PY and octahedral Mg exposed to the channel. From the thermal study it can be concluded that hydrophobicity of the clays increases and their thermal stability decreases as a result of the adsorption of the organic bases.

Infrared study of grinding kaolinite with alkali metal chlorides

Abstract Kaolinite was mechanically ground in the presence of NaCl, KCl, RbCl and CsCl and in their absence, and i.r. spectra were recorded after various periods of grinding. Changes in the intensity and sharpness of the absorption bands were interpreted using accepted assignments. The following effects were observed: 1. (1) Destruction of the kaolinite structure and formation of amorphous material. 2. (2) Solid state diffusion of atoms, particularly protons, leading to the formation of lattice defects. 3. (3) Delamination of the tactoid of kaolinite. 4. (4) Enhanced hydration. The relative weight and significance of these reactions depend on the alkali halide present. Thus, after grinding, different spectra are obtained with different alkali halides. In the presence of CsCl hydrogen bonds were formed between basal hydroxyls and sorbed water molecules.

Visible absorption spectroscopy study of the adsorption of Congo Red by montmorillonite

Abstract The adsorption of the anionic dye Congo Red (CR) by Na-, Cs-, Mg-, Cu-, Al- and Fe-montmorillonite was investigated by electronic spectroscopy. Spectra of the aqueous suspensions of different clay concentrations and different loadings were recorded. The spectra were curve fitted and were compared to spectra of aqueous solutions of CR at different pH values. Four bands representing anionic varieties and two representing protonated varieties of CR were identified in spectra of CR-treated Na-, Cs-, Mg-, Cu- and Al-montmorillonite. Spectra of CR-treated Fe-montmorillonite were slightly different, showing three bands representing anionic varieties and four representing protonated CR. The ratio between areas of bands, which represent the protonated varieties, and those representing the anionic varieties were determined showing correlation with the acidity of the metallic cation. The clay in the aqueous suspensions became coloured after the adsorption of CR. The following stainings were obtained, Na- and Mg-clay, red, Cs-clay, violet-red, Cu-clay, reddish-violet, Al-clay, dark violet and Fe-clay, dark blue. It appears that CR can serve as an indicator of the surface acidity of montmorillonite. The effects of aging on the sorption of the dye and on the surface-acidity of the CR-clay complex were investigated.

Sorption of rhodamine B by montmorillonite and laponite

Abstract The adsorption of rhodamine B by montmorillonite and laponite has been studied by visible (absorption and emission) and infrared spectroscopy, and X-ray diffraction. The dye is adsorbed as a uni-charged cation by a mechanism of cation exchange. The amount of this cation and consequently the degree of adsorption depend on pH and on the dye concentration. The adsorbed cationic dye is located in the interlayer space. Due to steric hindrance no π interactions occur between the clay and the aromatic compound and no metachromasy is observed.

THE STUDY OF THE DEHYDRATION AND DEHYDROXYLATION OF SMECTITEs BY EMANATION THERMAL ANALYSIS

The dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO4 network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.

Kinetic analysis of thermal dehydration and hydrolysis of MgCl2•6H2O by DTA and TG

The thermal decomposition of MgCl2·6H2O (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, IR, X-ray diffraction and chemical analysis of Mg and Cl. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgCl2·H2O and dehydrochloridization of magnesium hydroxy chlorides. Melting of the phases MgCl2·6H2O, MgCl2·4H2O and MgCl2 was also identified in the thermal curves. Thermal weight loss continued up to 800 °C in flowing air or nitrogen, but only up to 700 °C in static air. MgO was the end-product of thermal treatment in both cases.The kinetic parameters of the reaction, the activation energyE, pre-exponential factorA and apparent order of reactionb, were computed by several methods. The activation energy and the apparent reaction order of dehydration were found to increase with decreasing hydration number of the Mg. The dehydrochloridization process had the highest activation energy.ZusammenfassungDie thermische Zersetzung von MgCl2·6H2O (nicht und teilweise getrocknet) und die Kinetik dieses Prozesses wurden mittels DTA, TG, DTG, IR, Röntgendiffraktometrie und chemischer Analyse von Mg und Cl untersucht. Die im Verlaufe der thermischen Analyse vor sich gehenden Reaktionen sind Dehydratisierung (in Schritten), thermische Hydrolyse von MgCl2·H2O und Chlorwasserstoffaustritt aus Magnesiumhydroxychloriden. Das Schmelzen der Phasen MgCl2·6H2O, MgCl2·4H2O und MgCl2 ist in den thermischen Kurven ebenfalls zu erkennen. Im Luft- und Stickstoffstrom erfolgt ein Gewichtsverlust bis 800 °C, in statischer Luftatmosphäre dagegen nur bis 700 °C. MgO war in beiden Fällen Endprodukt der thermischen Behandlung. Die kinetischen Parameter der Reaktion (AktivierungsenergieE, präexponentieller FaktorA, scheinbare Reaktionsordnungb) wurden nach verschiedenen Methoden berechnet. Aktivierungsenergie und scheinbare Reaktionsordnung der Dehydratisierung nehmen mit abnehmendem Hydratationsgrad des Mg zu. Die Chlorwasserstoffabspaltung erfordert die höchste Aktivierungsenergie.РезюмеМетодом ДТА, ТГ, ДТГ, ИК спектроскопии, рентгеноструктурно го анализа и химического анализа было изучено термиче ское разложение гексагид рата хлористого магн ия (влажного и частично в ысушенного) и кинетик а процесса его разложения. Были и дентифицированы следующие реакции: де гидратация (ступенча тая), термический гидроли з моногидрата хлорида магния и деги дрохлорирование осн овной соли магния. На термически х кривых идентифицированы те мпературы плавления гексагидрата, тетраг идрата хлорида магни я и безводной соли. В дина мической атмосфере в оздуха и азота термическая по теря веса продолжалась до темп ературы 800 °C, тогда как в статической атмосфе ре воздуха-до 700 °C. B обоих случаях конечн ым продуктом разложе ния являлась окись магния. Несколь кими методами были расчит аны энергия активаци и, предэкспоненциальн ый множитель и кажущи йся порядок реакции. Уста новлено, что энергия а ктивации и кажущийся порядок ре акции дегидратации увелич иваются с уменьшение м числа гидратации магния. Пр оцесс дегидрохлорир ования имел наиболее высоко е значение энергии ак тивации.