Ferenc Szántó

Sorption and immersional wetting on clay minerals having modified surface: II. Interlamellar sorption and wetting on organic montmorillonites

Abstract Adsorption of methanol-benzene mixtures and heats of immersion have been investigated on the organic derivatives of montmorillonite. The surface of the mineral was modified by n-alkyl pyridinium and dimethyldihexadecyl ammonium ions. In the case of completely exchanged samples the adsorption capacity volumes agree with the interlamellar volumes calculated from X-ray diffraction data rather well. The organophilicity is characterized by the proportion of the nonpolar/polar surfaces. The specific enthalpies of immersion have been measured in methanol, benzene, and their mixtures. The immersion shows endothermic-exothermic or endothermic heat effects.

Sorption and immersional wetting on clay minerals having modified surface. I. Surface properties of nonswelling clay mineral organocomplexes

Abstract Adsorption of methanol-benzene mixtures and the immersional wetting properties have been investigated on nonswelling clay minerals with lamellar structure (kaolinite and illite) and on their organocomplexes obtained by hexadecyl-pyridinium cations (HDP+). It has been found that the surface modification can influence the selective liquid adsorption. To interpret unambiguously the extent of the surface modification the nonpolar-polar surface area ratio can be calculated from the sorption data. From the excess isotherms and the enthalpy of immersion the surface thermodynamic potential functions have been calculated. The changes of these functions and the equilibrium constant of the adsorption with the surface polarity is given. Adsorption capacity data and immersional wetting experiments indicate that the surface extension of these organocomplexes can change in some degree.

The pH-dependent colloidal stability of aqueous montmorillonite suspensions

Abstract The pH-dependent colloidal stability of aqueous montmorillonite suspensions was examined by coagulation and compression studies, and it was explained on the basis of calculations involving an ionization model and the classical DLVO theory. The intrinsic ionization constants (p K SOH =2.6 and p K TOH =6.4) and the ionizable site density ( N S =4.8·10 17 sites m −2 ) of montmorillonite prepared by ion exchange were determined experimentally. The total interaction energy as a function of 1:1 electrolyte concentration was calculated at different pH. The significant decrease of the stability of the suspensions with decreasing pH was verified experimentally. Suspensions at pH 2, 4 and 8 coagulated in the presence of 100, 200–250 and 350–400 mmol dm −3 NaCl, respectively. The values of V T,max relating to these concentrations are between 0.1 and 0.25 mJ m −2 , hardly differing from one another. The results of compression studies on sodium- and hydrogen-montmorillonite suspensions likewise demonstrated the theoretically expected differences.

Adsorption of liquid mixtures on bentonite and organophilic bentonite

Selective sorption of binary mixtures has been studied on bentonite and organophilic bentonite. Adsorption excess isotherms on these adsorbents have been determined for benzenen-n-heptane and alcohol-benzene mixtures, and the adsorption capacity of the components has been calculated by the analysis of the excess isotherms. The organocomplex swells only to a small extent in benzene-n-heptane mixtures, while in alcohol-benzene mixtures significant swelling and disaggregation occurs owing to positive adsorption of the alcohols. The results of adsorption measurements are concordant with the swelling and disaggregation characterized by sediment volume measurements.

Sorption and immersional wetting properties of palygorskite and its hexadecylpyridinium derivatives

Abstract Methods involving gas and liquid sorption and immersion microcalorimetry were used to study the surface properties of the clay mineral palygorskite and its derivatives in which the surface had been modified to various extents with the hexadecylpyridinium (HDP) cation. The sorption studies revealed that surface modification with this cationic surfactant blocks the micropores in the palygorskite silicate chains, whereupon the adsorption capacity decreases. An additional factor influencing the selective sorption of mixtures of benzene with various alcohols is the change in the polarity of the surface. The enthalpies of immersion showed that the solid-liquid interface interaction is altered by the adsorption of the HDP cation, i.e., by the decrease in polarity of the surface. An almost linear correlation was found between the molar enthalpies of immersion and a factor describing the polarity of the surface. Both the differences in adsorption of the various alcohols and the changes in the liquid sorption properties due to the surface modification were characterized with surface thermodynamic potential functions.

The liquid-crystal structure of adsorbed layers and the stability of dispersed systems in organic liquids

Abstract The adsorption of methanol—benzene and ethanol—cyclohexane mixtures has been studied on hydrophobic layer silicates made hydrophobic by cationic surfactants (C12–C18). X-ray diffraction measurements of these expanded systems gave the interlayer spacing and interlayer volumes. From the adsorption measurements and from the interlayer volumes the composition of the interlayer phases was determined. It was established that for a known concentration range of surfactant—alcohol—benzene (or cyclohexane) composition the adsorption layer had a smectic or nematic structure in the interlayer space. This layer can be produced without silicate lamellae for a specific concentration range with a small amount of water. A liquid-crystalline structure was shown to be present from polarization microscopy and small-angle X-ray diffraction measurements. At higher alcohol concentrations the adsorption layer was thinner and the lyotropic liquid-crystalline phase no longer existed. The well oriented adsorption layer broke down and the interlayer spacing became smaller.

Liquid sorption and immersional wetting on dealuminated Y-type zeolites

Abstract The adsorption and immersional wetting properties of Na-Y zeolite essentially change by dealumination of the zeolite. By studying the adsorption of alcohol-benzene and benzene- n -heptane mixtures it was found that the dealumination results in a decrease of the adsorption capacity of about 25% and in a depolarization of the surface. The decrease of the surface energy is also supported by microcalorimetric immersion measurements. The changes of excess free energy, excess enthalpy, and excess entropy accompanying the wetting process were calculated from the experimentally determined adsorption excess isotherms and immersion wetting data. The thermodynamic potential functions indicate that dealumination results in a considerable decrease of the sorption selectivity and of the surface energy of zeolite Y.

Effect of sodium chloride on interactions of fulvic acid and fulvate with montmorillonite

Abstract The interaction of montmorillonite and fulvic acid has been studied at various values of pH and 1 : 1 electrolyte concentrations. The fulvic acid was prepared from gallic acid by heterogeneous catalysis. The amounts adsorbed were determined from the decrease in solute concentration. The adsorption of fulvic acid on H-montmorillonite at pH of about 2.8 is higher than that of Na-fulvate on Na-montmorillonite at pH of about 7.5 in electrolyte-free systems. At low pH, a small amount of NaCl (10 or 20 mmol dm−3) had virtually the same effect on interaction as an amount of 200 or 500 mmol dm−3 at alkaline pH. The combined effect of the pH and NaCl was interpreted by calculating the surface charge, the potential, and the interaction energy of montmorillonite and humic substance particles by a simple model including the assumption of two widely different, intrinsic dissociation constants of the fulvic acid.